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Background Nursing home (NH) residents are prioritized for COVID-19 vaccination. We report monthly mortality, hospitalizations, and emergency department (ED) visit incidence rates (IRs) during 2010–2020 to provide context for COVID-19 vaccine safety assessments. Methods We observed outcomes among all NH residents in Ontario using administrative databases. IRs were calculated by month, sex, and age group. Comparisons between months were assessed using one-sample t-tests; comparisons by age and sex were assessed using chi-squared tests. Results From 2010 to 2019, there were 83,453 (SD: 652.4) NH residents per month, with an average of 2.3 (SD: 0.28) deaths, 3.1 (SD: 0.16) hospitalizations, and 3.6 (SD: 0.17) ED visits per 100 residents per month. From March to December 2020, mortality IRs were increased, but hospitalization and ED visit IRs were reduced (p Conclusion We identified consistent monthly mortality, hospitalization, and ED visit IRs during 2010–2019. Marked differences in these rates were observed during 2020, coinciding with the COVID-19 pandemic.

BACKGROUND: Nonpharmaceutical interventions remain the primary means of controlling severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) until vaccination coverage is sufficient to achieve herd immunity. We used anonymized smartphone mobility measures to quantify the mobility level needed to control SARS-CoV-2 (i.e., mobility threshold), and the difference relative to the observed mobility level (i.e., mobility gap). METHODS: We conducted a time-series study of the weekly incidence of SARS-CoV-2 in Canada from Mar. 15, 2020, to Mar. 6, 2021. The outcome was weekly growth rate, defined as the ratio of cases in a given week versus the previous week. We evaluated the effects of average time spent outside the home in the previous 3 weeks using a log-normal regression model, accounting for province, week and mean temperature. We calculated the SARS-CoV-2 mobility threshold and gap. RESULTS: Across the 51-week study period, a total of 888 751 people were infected with SARS-CoV-2. Each 10% increase in the mobility gap was associated with a 25% increase in the SARS-CoV-2 weekly case growth rate (ratio 1.25, 95% confidence interval 1.20–1.29). Compared to the prepandemic baseline mobility of 100%, the mobility threshold was highest in the summer (69%; interquartile range [IQR] 67%–70%), and dropped to 54% in winter 2021 (IQR 52%–55%); a mobility gap was present in Canada from July 2020 until the last week of December 2020. INTERPRETATION: Mobility strongly and consistently predicts weekly case growth, and low levels of mobility are needed to control SARS-CoV-2 through spring 2021. Mobility measures from anonymized smartphone data can be used to guide provincial and regional loosening and tightening of physical distancing measures.

Background Within-household transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection has been identified as one of the main sources of spread of coronavirus disease 2019 (COVID-19) after lockdown restrictions and self-isolation guidelines are implemented. Secondary attack rates among household contacts are estimated to be 5–10 times higher than among non-household contacts, but it is unclear which individuals are more prone to transmit infection within their households. Methods Using address matching, a cohort was assembled of all individuals with laboratory-confirmed COVID-19 residing in private households in Ontario, Canada. Descriptive analyses were performed to compare characteristics of cases in households that experienced secondary transmission versus those that did not. Logistic regression models were fit to determine index case characteristics and neighborhood characteristics associated with transmission. Results Between January and July 2020, there were 26 714 individuals with COVID-19 residing in 21 226 households. Longer testing delays (≥5 vs 0 days; odds ratio [OR], 3.02; 95% confidence interval [CI], 2.53–3.60) and male gender (OR, 1.28; 95% CI, 1.18–1.38) were associated with greater odds of household secondary transmission, while being a healthcare worker (OR, .56; 95% CI, .50–.62) was associated with lower odds of transmission. Neighborhoods with larger average family size and a higher proportion of households with multiple persons per room were also associated with greater odds of transmission. Conclusions It is important for individuals to get tested for SARS-CoV-2 infection as soon as symptoms appear, and to isolate away from household contacts; this is particularly important in neighborhoods with large family sizes and/or crowded households.

Introduction In Ontario, Canada, parents have the responsibility to report their child’s routine infant and childhood vaccines to the provincial immunization registry (the Digital Health Immunization Repository; DHIR) without healthcare provider validation. Despite its use in routine immunization coverage monitoring, no study has previously examined the completeness of immunization data within the DHIR. Methods We assessed the completeness of DHIR immunizations, as compared to immunizations within the Electronic Medical Records—Primary Care (EMRPC) database, also known as EMRALD, a network of family physician electronic medical records (EMRs). We linked client records from the DHIR and EMRPC to a centralized population file. To create the study cohort, we examined children born during 2005–2008 and further defined the cohort based on those rostered to an EMRPC physician, visit criteria to ensure ongoing care by an EMRPC provider, and school attendance in Ontario at age 7. We calculated up-to-date (UTD) immunization coverage at age 7 for individual vaccines and overall using data from the DHIR and EMRPC separately, and compared the estimates. Results The analytic cohort to assess DHIR data completeness included 2,657 children. Overall UTD coverage (all vaccines assessed) was 82.0% in the DHIR and 67.6% in EMRPC. UTD coverage was higher in the DHIR for all vaccines assessed individually, with the exception of meningococcal C conjugate vaccine (difference = 0.3%). After excluding two EMRPC sites with irregularities in immunization data, the difference in overall UTD coverage between systems decreased from 14.4% to 6.6% Interpretation These results validate the use of DHIR for coverage assessment but also suggest that bidirectional exchange of immunization information has the potential to increase immunization data completeness in both systems.

As of January 22, 2020, "disease caused by a novel coronavirus" became a reportable disease of public health significance in Ontario. Public health units were provided with guidance on the entry of patients tested for severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), the virus causing 2019 coronavirus disease (COVID-19), into the provincial public health information system. Between January 22 and February 22, 2020, there were 359 individuals who had a negative test result recorded and three confirmed cases of COVID-19. Of those who tested negative, 51% were female and 71% were under 50 years of age. The most common symptoms reported were cough (55%), fever (37%) and sore throat (35%). The majority were tested within three days of symptom onset, but over one-quarter tested more than seven days after symptom onset. Over the first month of reportability, reported travel history shifted from China to an increasing proportion with travel outside of China.

Setting Syndemics occur when two or more health conditions interact to increase morbidity and mortality and are exacerbated by social, economic, environmental, and political factors. Routine provincial surveillance in Ontario assesses and reports on the epidemiology of single infectious diseases separately. Therefore, we aimed to develop a method that allows disease overlaps to be examined routinely as a path to better understanding and addressing syndemics in Ontario. Intervention We extracted data for individuals with a record of chlamydia, gonorrhea, infectious syphilis, hepatitis B and C, HIV/AIDS, invasive group A streptococcal disease (iGAS), or tuberculosis in Ontario’s reportable disease database from 1990 to 2018. We transformed the data into a person-based integrated surveillance dataset retaining individuals (clients) with at least one record between 2006 and 2018. Outcomes The resulting dataset had 659,136 unique disease records among 470,673 unique clients. Of those clients, 23.1% had multiple disease records with 50 being the most for one client. We described the frequency of disease overlaps; for example, 34.7% of clients with a syphilis record had a gonorrhea record. We quantified known overlaps, finding 1274 clients had gonorrhea, infectious syphilis, and HIV/AIDS records, and potentially emerging overlaps, finding 59 clients had HIV/AIDS, hepatitis C, and iGAS records. Implications Our novel person-based integrated surveillance dataset represents a platform for ongoing in-depth assessment of disease overlaps such as the relative timing of disease records. It enables a more client-focused approach, is a step towards improved characterization of syndemics in Ontario, and could inform other jurisdictions interested in adopting similar approaches.

Epidemic curves are used by decision makers and the public to infer the trajectory of the COVID-19 pandemic and to understand the appropriateness of current response measures. Symptom onset date is commonly used to date cases on the epidemic curve in public health reports and dashboards. However, third-party trackers often plot cases on the epidemic curve by the date they were publicly reported by the public health authority. These two curves create very different impressions of epidemic progression. On April 1, the epidemic curve for Ontario, Canada based on public reporting date showed an accelerating epidemic, whereas the curve based on a proxy variable for symptom onset date showed a rapidly declining epidemic. This illusory downward trend (the "ghost trend") is a feature of epidemic curves anchored using date variables earlier in time than the date a case was publicly reported, such as symptom onset date or sample collection date. This is because newly discovered cases are backdated, creating a perpetual downward trend in incidence due to incomplete data in the most recent days. Public reporting date is not subject to backdating bias and can be used to visualize real-time epidemic curves meant to inform the public and policy makers.

Objective To estimate the effectiveness of mRNA covid-19 vaccines against symptomatic infection and severe outcomes (hospital admission or death). Design Test negative design study. Setting Ontario, Canada between 14 December 2020 and 19 April 2021. Participants 324 033 community dwelling people aged ≥16 years who had symptoms of covid-19 and were tested for SARS-CoV-2. Interventions BNT162b2 (Pfizer-BioNTech) or mRNA-1273 (Moderna) vaccine. Main outcome measures Laboratory confirmed SARS-CoV-2 by reverse transcription polymerase chain reaction (RT-PCR) and hospital admissions and deaths associated with SARS-CoV-2 infection. Multivariable logistic regression was adjusted for personal and clinical characteristics associated with SARS-CoV-2 and vaccine receipt to estimate vaccine effectiveness against symptomatic infection and severe outcomes. Results Of 324 033 people with symptoms, 53 270 (16.4%) were positive for SARS-CoV-2 and 21 272 (6.6%) received at least one dose of vaccine. Among participants who tested positive, 2479 (4.7%) were admitted to hospital or died. Vaccine effectiveness against symptomatic infection observed ≥14 days after one dose was 60% (95% confidence interval 57% to 64%), increasing from 48% (41% to 54%) at 14-20 days after one dose to 71% (63% to 78%) at 35-41 days. Vaccine effectiveness observed ≥7 days after two doses was 91% (89% to 93%). Vaccine effectiveness against hospital admission or death observed ≥14 days after one dose was 70% (60% to 77%), increasing from 62% (44% to 75%) at 14-20 days to 91% (73% to 97%) at ≥35 days, whereas vaccine effectiveness observed ≥7 days after two doses was 98% (88% to 100%). For adults aged ≥70 years, vaccine effectiveness estimates were observed to be lower for intervals shortly after one dose but were comparable to those for younger people for all intervals after 28 days. After two doses, high vaccine effectiveness was observed against variants with the E484K mutation. Conclusions Two doses of mRNA covid-19 vaccines were observed to be highly effective against symptomatic infection and severe outcomes. Vaccine effectiveness of one dose was observed to be lower, particularly for older adults shortly after the first dose.

ObjectivesThe objective of our study was to estimate the rate of workplace outbreak-associated cases of COVID-19 by industry in labour market participants aged 15-69 years who reported working the majority of hours outside the home in Ontario, Canada.MethodsWe conducted a population based cross-sectional study of COVID-19 workplace outbreaks and associated-cases reported in Ontario between April 1, 2020 and March 31, 2021. All outbreaks were manually classified into two digit North American Industry Classification System (NAICS) codes. We obtained denominator data from the Statistics Canada Labour Force Survey in order to estimate the incidence of outbreak-associated cases per 100,000,000 hours amongst individuals who reported the majority of hours were worked outside the home. We performed this analysis across industries and in three distinct time periods.ResultsOverall, 12% of cases were attributed to workplace outbreaks among working age adults across our study period. While incidence varied across the time periods, the five industries with the highest incidence rates across our study period were agriculture; healthcare and social assistance; food manufacturing; educational services; and, transportation and warehousing.ConclusionsCertain industries have consistently increased incidence of COVID-19 over the course of the pandemic. These results may assist in ongoing efforts to reduce transmission of COVID-19, by prioritizing resources, as well as industry-specific guidance, vaccination, and public health messaging.

Background SARS-CoV-2 variants of concern (VOC) are more transmissible and have the potential for increased disease severity and decreased vaccine effectiveness. We sought to estimate the effectiveness of BNT162b2 (Pfizer-BioNTech), mRNA-1273 (Moderna), and ChAdOx1 (AstraZeneca) vaccines against symptomatic SARS-CoV-2 infection and severe outcomes (COVID-19 hospitalization or death) caused by the Alpha (B.1.1.7), Beta (B.1.351), Gamma (P.1), and Delta (B.1.617.2) VOCs during December 2020 to May 2021. Methods We conducted a test-negative design study using linked population-wide vaccination, laboratory testing, and health administrative databases in Ontario, Canada. Findings Against symptomatic infection caused by Alpha, vaccine effectiveness with partial vaccination (≥14 days after dose 1) was higher for mRNA-1273 (83%) than BNT162b2 (66%) and ChAdOx1 (64%), and full vaccination (≥7 days after dose 2) increased vaccine effectiveness for BNT162b2 (89%) and mRNA-1273 (92%). Protection against symptomatic infection caused by Beta/Gamma was also higher with partial vaccination for mRNA-1273 (77%) than BNT162b2 (60%) and ChAdOx1 (48%), and full vaccination increased effectiveness for BNT162b2 (84%). Against Delta, vaccine effectiveness after partial vaccination tended to be lower compared to Alpha for mRNA-1273 (72% vs. 83%) and BNT162b2 (56% vs. 66%), but was similar to Alpha for ChAdOx1 (67% vs. 64%). Full vaccination with BNT162b2 increased protection against Delta (87%) to levels comparable to Alpha (89%) and Beta/Gamma (84%). Vaccine effectiveness against hospitalization or death caused by all VOCs was generally higher than for symptomatic infection after partial vaccination for all three vaccines. Interpretation Our findings suggest that even a single dose of these 3 vaccines provide substantial protection against these 4 VOCs, and 2 doses likely provide higher protection. Jurisdictions facing vaccine supply constraints might consider delaying second doses to more rapidly achieve greater overall population protection.

Background Many countries recommend influenza vaccination during pregnancy. Despite this recommendation, influenza vaccine among pregnant individuals remains under-utilized and uptake varies by country. Factors associated with influenza vaccine uptake during pregnancy may also vary across countries. Methods As members of the Pregnancy Influenza Vaccine Effectiveness Network (PREVENT), five sites from four countries (Australia, Canada, Israel, and the United States) retrospectively identified cohorts of individuals aged 18–50 years who were pregnant during pre-defined influenza seasons. Influenza vaccine coverage estimates were calculated for the 2010–11 through 2015–16 northern hemisphere and the 2012 through 2015 southern hemisphere influenza seasons, by site. Sites used electronic health records, administrative data, and immunization registries to collect information on pregnancy, health history, demographics, and vaccination status. Each season, vaccination coverage was calculated as the percentage of individuals who received influenza vaccine among the individuals in the cohort that season. Characteristics were compared between those vaccinated and unvaccinated, by site. Results More than two million pregnancies were identified over the study period. Influenza vaccination coverage ranged from 5% to 58% across sites and seasons. Coverage increased consistently over the study period at three of the five sites (Western Australia, Alberta, and Israel), and was highest in all seasons at the United States study site (39–58%). Associations with vaccination varied by country and across seasons; where available, parity >0, presence of a high-risk medical condition, and urban residence were consistently associated with increased likelihood of vaccination. Conclusions Though increasing, uptake of influenza vaccine among pregnant individuals remains lower than recommended. Coverage varied substantially by country, suggesting an ongoing need for targeted strategies to improve influenza vaccine uptake in this population.

We compared secondary attack rates in households with B.1.1.7 variant of concern (VOC) versus non-VOC index cases in a matched cohort in Ontario, Canada. The secondary attack rate for VOC index cases was 1.31 times higher than non-VOC index cases. This increase was particularly accentuated for asymptomatic or presymptomatic index cases.

ObjectivesTo estimate the effectiveness of mRNA COVID-19 vaccines against symptomatic infection and severe outcomes.DesignWe applied a test-negative design study to linked laboratory, vaccination, and health administrative databases, and used multivariable logistic regression adjusting for demographic and clinical characteristics associated with SARS-CoV-2 and vaccine receipt to estimate vaccine effectiveness (VE) against symptomatic infection and severe outcomes.SettingOntario, Canada between 14 December 2020 and 19 April 2021.ParticipantsCommunity-dwelling adults aged ≥16 years who had COVID-19 symptoms and were tested for SARS-CoV-2.InterventionsPfizer-BioNTech’s BNT162b2 or Moderna’s mRNA-1273 vaccine.Main outcome measuresLaboratory-confirmed SARS-CoV-2 by RT-PCR; hospitalization/death associated with SARS-CoV-2 infection.ResultsAmong 324,033 symptomatic individuals, 53,270 (16.4%) were positive for SARS-CoV-2 and 21,272 (6.6%) received ≥1 vaccine dose. Among test-positive cases, 2,479 (4.7%) had a severe outcome. VE against symptomatic infection ≥14 days after receiving only 1 dose was 60% (95%CI, 57 to 64%), increasing from 48% (95%CI, 41 to 54%) at 14–20 days after the first dose to 71% (95%CI, 63 to 78%) at 35–41 days. VE ≥7 days after 2 doses was 91% (95%CI, 89 to 93%). Against severe outcomes, VE ≥14 days after 1 dose was 70% (95%CI, 60 to 77%), increasing from 62% (95%CI, 44 to 75%) at 14–20 days to 91% (95%CI, 73 to 97%) at ≥35 days, whereas VE ≥7 days after 2 doses was 98% (95%CI, 88 to 100%). For adults aged ≥70 years, VE estimates were lower for intervals shortly after receiving 1 dose, but were comparable to younger adults for all intervals after 28 days. After 2 doses, we observed high VE against E484K-positive variants.ConclusionsTwo doses of mRNA COVID-19 vaccines are highly effective against symptomatic infection and severe outcomes. Single-dose effectiveness is lower, particularly for older adults shortly after the first dose.

Supplemental Digital Content is available in the text, Objective: To analyze workplace outbreaks by industry sector in the first wave of the pandemic, and associated household cases. Methods: Number, size, and duration of outbreaks were described by sector, and outbreak cases were compared to sporadic cases in the same time frame. Address matching identified household cases with onset ≥2 days before, ≥2 days after, or within 1 day of the workplace outbreak case. Results: There were 199 outbreaks with 1245 cases, and 68% of outbreaks and 80% of cases belonged to (1) Manufacturing, (2) Agriculture, Forestry, Fishing, Hunting, (3) Transportation and Warehousing. There were 608 household cases associated with 339 (31%) outbreak cases, increasing the burden of illness by 56%. Conclusions: Workplace outbreaks primarily occurred in three sectors. Prevention measures should target industry sectors at risk to prevent spread in and out of the workplace.

PURPOSE Seasonal influenza vaccination is recommended for patients with cancer despite concerns of disease or treatment-associated immunosuppression. The objective of this study was to evaluate vaccine effectiveness (VE) against laboratory-confirmed influenza for patients with cancer. PATIENTS AND METHODS We conducted an observational test-negative design study of previously diagnosed patients with cancer 18 years of age and older who underwent influenza testing during the 2010-2011 to 2015-2016 influenza seasons in Ontario, Canada. We linked individual-level cancer registry, respiratory virus testing, and health administrative data to identify the study population and outcomes. Vaccination status was determined from physician and pharmacist billing claims. We used multivariable logistic regression to estimate VE, adjusting for age, sex, rurality, income quintile, cancer characteristics, chemotherapy exposure, comorbidities, previous health care use, influenza season, and calendar time. RESULTS We identified 26,463 patients with cancer who underwent influenza testing, with 4,320 test-positive cases (16%) and 11,783 (45%) vaccinated. Mean age was 70 years, 52% were male, mean time since diagnosis was 6 years, 69% had solid tumor malignancies, and 23% received active chemotherapy. VE against laboratory-confirmed influenza was 21% (95% CI, 15% to 26%), and VE against laboratory-confirmed influenza hospitalization was 20% (95% CI, 13% to 26%). For patients with solid tumor malignancies, VE was 25% (95% CI, 18% to 31%), compared with 8% (95% CI, –5% to 19%) for patients with hematologic malignancies ( P = .015). Active chemotherapy usage did not significantly affect VE, especially among patients with solid tumor cancer. CONCLUSION Our results support recommendations for influenza vaccination for patients with cancer. VE was decreased for patients with hematologic malignancies, and there was no significant difference in VE among patients with solid tumor cancer receiving active chemotherapy. Strategies to optimize influenza prevention among patients with cancer are warranted.

Background Annual influenza immunization is recommended for people with chronic obstructive pulmonary disease (COPD) by all major COPD clinical practice guidelines. We sought to determine the seasonal influenza vaccine effectiveness (VE) against laboratory-confirmed influenza-associated hospitalizations among older adults with COPD. Methods We conducted a test-negative study of influenza VE in community-dwelling older adults with COPD in Ontario, Canada using health administrative data and respiratory specimens collected from patients tested for influenza during the 2010–11 to 2015–16 influenza seasons. Influenza vaccination was ascertained from physician and pharmacist billing claims. Multivariable logistic regression was used to estimate the adjusted odds ratio of influenza vaccination in people with, compared to those without, laboratory-confirmed influenza. Results Receipt of seasonal influenza vaccine was associated with an adjusted 22% (95% confidence interval [CI], 15%–27%) reduction in laboratory-confirmed influenza-associated hospitalization. Adjustment for potential misclassification of vaccination status increased this to 43% (95% CI, 35%–52%). Vaccine effectiveness was not found to vary by patient- or influenza-related variables. Conclusions During the studied influenza seasons, influenza vaccination was at least modestly effective in reducing laboratory-confirmed influenza-associated hospitalizations in people with COPD. The imperfect effectiveness emphasizes the need for better influenza vaccines and other preventive strategies.

Background Linking data on laboratory specimens collected during clinical practice with health administrative data permits highly powered vaccine effectiveness (VE) studies to be conducted at relatively low cost, but bias from using convenience samples is a concern. We evaluated the validity of using such data for estimating VE. Methods We created the Flu and Other Respiratory Viruses Research (FOREVER) Cohort by linking individual-level data on respiratory virus laboratory tests, hospitalizations, emergency department visits, and physician services. For community-dwelling adults aged > 65 years, we assessed the presence and magnitude of information and selection biases, generated VE estimates under various conditions, and compared our VE estimates with those from other studies. Results We included 65,648 unique testing episodes obtained from 54,434 individuals during the 2010–11 to 2015–16 influenza seasons. To examine information bias, we found the proportion testing positive for influenza for patients with unknown interval from illness onset to specimen collection was more similar to patients for whom illness onset date was ≤ 7 days before specimen collection than to patients for whom illness onset was > 7 days before specimen collection. To assess the presence of selection bias, we found the likelihood of influenza testing was comparable between vaccinated and unvaccinated individuals, although the adjusted odds ratios were significantly greater than 1 for some healthcare settings and during some influenza seasons. Over 6 seasons, VE estimates ranged between 36% (95%CI, 27–44%) in 2010–11 and 5% (95%CI, –2, 11%) in 2014–15. VE estimates were similar under a range of conditions, but were consistently higher when accounting for misclassification of vaccination status through a quantitative sensitivity analysis. VE estimates from the FOREVER Cohort were comparable to those from other studies. Conclusions Routinely collected laboratory and health administrative data contained in the FOREVER Cohort can be used to estimate influenza VE in community-dwelling older adults.

IMPORTANCEHigher secondary attack rates related to variant of concern (VOC) index cases have been reported, but have not been explored within households, which continue to be an important source of coronavirus disease 2019 (COVID-19) transmissionOBJECTIVETo compare secondary attack rates in households with VOC versus non-VOC index cases.DESIGNA retrospective cohort study of household index cases reported from February 7 – 27, 2021. A propensity-score matched cohort was derived to calculate adjusted estimates.SETTINGOntario, Canada.PARTICIPANTSA population-based cohort of all private households with index cases. We excluded cases in congregate settings, as well as households with one individual or with >1 case with the same earliest symptom onset date.EXPOSUREVOC status, defined as either individuals confirmed as B.1.1.7 using whole genome sequencing or those that screened positive for the N501Y mutation using real-time PCR.MAIN OUTCOME AND MEASUREHousehold secondary attack rate, defined as the number of household secondary cases that occurred 1-14 days after the index case divided by the total number of household secondary contacts.RESULTSWe included 1,259 index VOC and non-VOC cases in the propensity score-matched analysis. The secondary attack rate for VOC index cases in this matched cohort was 1.31 times higher than non-VOC index cases (RR=1.31, 95%CI 1.14-1.49), similar to the unadjusted estimate. In stratified analyses, the higher secondary attack rate for VOC compared to non-VOC index cases was accentuated for asymptomatic index cases (RR=1.91, 95% CI 0.96-3.80) and presymptomatic cases (RR=3.41, 95%CI 1.13-10.26)CONCLUSIONS AND RELEVANCEThis study provides strong evidence of increased transmissibility in households due to VOCs and suggests that asymptomatic and pre-symptomatic transmission may be of particular importance for VOCs. Our study suggests that more aggressive public health measures will be needed to control VOCs and that ongoing research is needed to understand mechanisms of VOC transmissibility to curb their associated morbidity and mortality.

BACKGROUNDAs a result of low numbers of pediatric cases early in the COVID-19 pandemic, pediatric household transmission of SARS-CoV-2 remains an understudied topic. This study sought to determine whether there are differences in the odds of household transmission for younger children compared to older children.METHODSWe assembled a cohort of all individuals in Ontario, Canada with laboratory-confirmed SARS-CoV-2 infection between June 1 and December 31, 2020. The cohort was restricted to individuals residing in private households (N=132,232 cases in 89,191 households), identified through an address matching algorithm. Analysis focused on households in which the index case was aged RESULTSA total of 6,280 households had pediatric index cases, and 1,717 (27.3%) experienced secondary transmission. Children aged 0-3 years had the highest odds of household transmission compared to children aged 14-17 years (model adjusted for gender, month of disease onset, testing delay, and average family size: 1.43, 95% CI: 1.17-1.75). This association was similarly observed in sensitivity analyses defining secondary cases as 2-14 days or 4-14 days after the index case, and stratified analyses by presence of symptoms, association with a school/childcare outbreak, or school/childcare reopening. Children aged 4-8 years and 9-13 years also had increased odds of transmission (4-8: 1.40, 95% CI: 1.18-1.67; 9-13: 1.13, 95% CI: 0.97-1.32).CONCLUSIONSThis study suggests that younger children are more likely to transmit SARS-CoV-2 infection compared to older children, and the highest odds of transmission was observed for children aged 0-3 years. Differential infectivity of pediatric age groups has implications for infection prevention controls within households, as well as schools/childcare, to minimize risk of household secondary transmission.

Background. Nursing home (NH) residents have been disproportionately affected by the coronavirus disease 2019 (COVID-19) pandemic and are prioritized for vaccination. NH residents are generally at increased risk of poor outcomes due to advanced age, frailty, and complex health conditions. We report monthly incidence rates of deaths, hospitalizations, and emergency department (ED) visits during ten pre-pandemic years (2010-2019) and 2020 to provide context for assessments of COVID-19 vaccine safety in NH residents. Methods. We observed deaths, hospitalizations, and ED visits among all Ontarians living in NHs using health administrative databases. Monthly incidence rates were calculated by month, by sex, and by age group. Direct comparisons between months were assessed using one-sample t-tests; direct comparisons by age and sex were assessed using chi-squared tests. Results. From January 1, 2010 through December 31, 2019, there were, on average, 83,453 (SD: 652.4) Ontarians living in NHs in any given month, with an average of 2.3 (SD: 0.28) deaths, 3.1 (SD: 0.16) hospitalizations, and 3.6 (SD: 0.17) ED visits per 100 residents per month. Mortality rates were higher for men (p

BackgroundMinimizing delays in disease identification and reporting improves the timeliness of surveillance data, and can reduce transmission of COVID-19. Our study investigates factors associated with timely testing and reporting of COVID-19 during the first pandemic wave in one province of Canada.MethodsWe identified all persons with confirmed SARS-CoV-2 infection residing in private households across the largest province of Canada, Ontario from the date of the first confirmed case in Ontario (January 25) to July 19, 2020. Our primary outcomes consisted of: (1) specimen collection within 1 day of symptom onset (test seeking), (2) test result reported to local public health within 1 day of specimen collection (test turnaround), and (3) entry of case data into the provincial database within 1 day of reporting test results (reporting). We examined 14 covariates including eight case characteristics, and six neighborhood characteristics. In addition to descriptive measures, logistic regression models were fitted. Unadjusted models included the covariate alone, while adjusted models included age, gender, month, and region.FindingsAmong 27,198 COVID-19 cases from January 25 2020 to July 19 2020, 28·7% had timely test seeking, 40·2% had timely test turnaround, and 75·5% had timely reporting. Male gender had lower odds of timely test seeking (adjusted odds ratio [aOR] 0·79 [95% CI: 0·74-0·85]) compared to females. Healthcare worker status (aOR 2·77 [95% CI: 2·52-3·05] compared to non-healthcare workers), and age ≥80 years (aOR 1·59 [95% CI: 1·33-1·91] compared to 40-59 year olds) were associated with timely test seeking. Specimen collection on Fridays and Saturdays (aOR 0·88 [95% CI: 0·79-0·98], aOR 0·83 [95% CI: 0·74-0·92] respectively, compared to Wednesdays) had lower odds of timely test turnaround. Urban areas (aOR 1·55 [95% CI: 1·41-1·70] compared to rural areas) were associated with timely test turnaround. Urban areas (aOR 0·79 [95% CI: 0·70-0·89] compared to rural areas) were less likely to have timely reporting.InterpretationIndividual, neighborhood, and administrative factors are associated with timely testing and reporting of SARS-CoV-2 infections. These findings present considerations for developing targeted strategies to minimize delays and improve timely testing and reporting of SARS-CoV-2 infections.FundingThis study was funded by Public Health Ontario.Research in ContextEvidence before this studyWe searched PubMed and medRxiv up to November 30 2020 to identify studies examining the impact of delays in the disease reporting process on the public health response to COVID-19. We used the search terms (“2019-nCoV” OR “COVID-19” OR “SARS-CoV-2”) AND (“delays” OR “timely” OR “reporting” OR “test” OR “turnaround”), and reviewed reference lists of any relevant articles in the original search. Numerous modeling studies have highlighted the importance of timely testing and reporting to effectively control the spread of COVID-19. Additional studies have also identified delays of only 1 day in testing were associated with increased risk of secondary transmission within households. However no study has described the multiple delays in the disease reporting process of COVID-19 and examined factors associated with timely disease reporting using a large population cohort.Added value of this studyOur study described timely test seeking, test turnaround, and reporting for laboratory-confirmed COVID-19 cases in Ontario, Canada and identified associated individual, neighbourhood, and administrative factors. To the best of our knowledge, this study is the first to describe detailed delays in the disease reporting process of COVID-19 and identified associated factors using a large population cohort.Implications of all the available evidenceNumerous individual, neighborhood, and administrative characteristics are associated with timely testing and reporting of COVID-19. These identified factors may be used to develop strategies such as broadened test access, prioritization of vulnerable populations, and increased testing capacity to reduce delays in testing and reporting and improve the effectiveness of public health response to COVID-19.

BackgroundNon-pharmaceutical interventions remain a primary means of suppressing COVID-19 until vaccination coverage is sufficient to achieve herd immunity. We used anonymized smartphone mobility measures in seven Canadian provinces to quantify the mobility level needed to suppress COVID-19 (mobility threshold), and the difference relative to current mobility levels (mobility gap).MethodsWe conducted a longitudinal study of weekly COVID-19 incidence from March 15, 2020 to January 16, 2021, among provinces with 20 COVID-19 cases in at least 10 weeks. The outcome was weekly growth rate defined as the ratio of current cases compared to the previous week. We examined the effects of average time spent outside the home (non-residential mobility) in the prior three weeks using a lognormal regression model accounting for province, season, and mean temperature. We calculated the COVID-19 mobility threshold and gap.ResultsAcross the 44-week study period, a total of 704,294 persons were infected with COVID-19. Non-residential mobility dropped rapidly in the spring and reached a median of 36% (IQR: 31,40) in April 2020. After adjustment, each 5% increase in non-residential mobility was associated with a 9% increase in the COVID-19 weekly growth rate (ratio=1.09, 95%CI: 1.07,1.12). The mobility gap increased through the fall months, which was associated with increasing case growth.InterpretationMobility strongly and consistently predicts weekly case growth, and low levels of mobility are needed to control COVID-19 through winter 2021. Mobility measures from anonymized smartphone data can be used to guide the provincial and regional implementation and loosening of physical distancing measures.

Older adults are at increased risk of herpes zoster (HZ) and post-herpetic neuralgia (PHN) and HZ vaccines are available to help prevent infection. The objective of our study was to provide updated data on incidence of HZ and PHN related to clinical and demographic factors in older adults to inform immunization practices. We conducted a population-based, retrospective cohort study and included all cases of HZ seen in outpatient, emergency department, and hospital settings for adults aged 65 years and over between April 1, 2002 to August 31, 2016 in Ontario, Canada. We calculated the incidence of HZ and PHN, and estimated the proportion within each subgroup that developed PHN. We also assessed incidence by neighbourhood-level income quintile before and after the availability of vaccine for private purchase. The average annual incidence of HZ in any setting was 59.0 per 10,000 older adults, with higher incidence in outpatient as opposed to hospital settings. Incidence was higher in the oldest age groups, females, and those classified as immunocompromised or frail. Relative to the pre-vaccine era, the disparities in incidence of HZ by neighbourhood-level income increased, with higher rates of HZ and PHN seen in those residing in lower income quintiles. Additional prevention efforts should be targeted toward adults who are immunocompromised, frail, and those living in lower socioeconomic quintiles. Future work should assess the impact of the zoster vaccine program with a particular focus on equity in the publicly-funded era.

Background: Co-infections of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) with respiratory viruses, bacteria and fungi have been reported to cause a wide range of illness. Objectives: We assess the prevalence of co-infection of SARS-CoV-2 with seasonal respiratory viruses, document the respiratory viruses detected among individuals tested for SARS-CoV-2, and describe characteristics of individuals with respiratory virus co-infection detected. Methods: Specimens included in this study were submitted as part of routine clinical testing to Public Health Ontario Laboratory from individuals requiring testing for SARS-CoV-2 and/or seasonal respiratory viruses. Results: Co-infection was detected in a smaller proportion (2.5%) of individuals with laboratory confirmed SARS-CoV-2 than those with seasonal respiratory viruses (4.3%), this difference was not significant. Individuals with any respiratory virus co-infection were more likely to be younger than 65 years of age and male than those with single infection. Those with SARS-CoV-2 co-infection manifested mostly mild respiratory symptoms. Conclusions: Findings of this study may not support routine testing for seasonal respiratory viruses among all individuals tested for SARS-CoV-2, as they were rare during the study period nor associated with severe disease. However, testing for seasonal respiratory viruses should be performed in severely ill individuals, in which detection of other viruses may assist with patient management.

Background: We estimated the effectiveness of BNT162b2 and mRNA-1273 vaccines among residents of Ontario, Canada, where a policy to use an up to 16-week interval between doses was adopted in March 2021. Methods: We conducted a test-negative design study using linked province-wide laboratory, vaccination, and health administrative datasets. We included symptomatic individuals tested for SARS-CoV-2 by RT-PCR between 14 December 2020 and 19 April 2021. Study outcomes included symptomatic infection and associated severe outcomes (hospitalization or death). We estimated adjusted vaccine effectiveness (aVE) using multivariable logistic regression. Findings: Among 324,033 symptomatic tested individuals, 53,270 (16·4%) were positive for SARS-CoV-2 and 21,272 (6·6%) had received ≥1 dose of mRNA vaccine. Among test-positive cases, 2,479 (4·7%) had a severe outcome. aVE against symptomatic infection ≥14 days after receiving only 1 dose was 60% (95%CI, 57–64%), increasing from 48% (95%CI, 41–54%) at 14–20 days after the first dose to 71% (95%CI, 63–78%) at 35–41 days. aVE ≥7 days after receiving 2 doses was 91% (95%CI, 89–93%). Against severe outcomes, aVE ≥14 days after receiving 1 dose was 70% (95%CI, 60–77%) and aVE ≥7 days after receiving 2 doses was 98% (95%CI, 88–100%). We observed lower aVE against both outcomes after receiving 1 dose for adults aged ≥70 years, but aVE estimates for older adults were comparable to younger adults after 28 days. After 2 doses, we observed high aVE against E484K-positive variants. Interpretation: Our findings suggest that 2 doses of BNT162b2 and mRNA-1273 vaccines are highly effective against both symptomatic infection and associated severe outcomes for all circulating variants, with effectiveness lower after only a single dose, particularly for older adults shortly after the first dose. Funding Information: Canadian Institutes of Health Research, Public Health Agency of Canada, Ontario Ministries of Health and Long-Term Care. Declaration of Interests: KW is CEO of CANImmunize and serves on the data safety board for the Medicago COVID-19 vaccine trial. SMM has received unrestricted research grants from Merck, GlaxoSmithKline, Sanofi Pasteur, Pfizer, and Roche-Assurex for unrelated studies. SMM has received fees as an advisory board member for GlaxoSmithKline, Merck, Pfizer, Sanofi Pasteur, and Seqirus. CHR has received an unrestricted research grant from Pfizer for an unrelated study. The other authors declare no conflicts of interest. Ethics Approval Statement: ICES is a prescribed entity under Ontario’s Personal Health Information Protection Act (PHIPA). Section 45 of PHIPA authorizes ICES to collect personal health information, without consent, for the purpose of analysis or compiling statistical information with respect to the management of, evaluation or monitoring of, the allocation of resources to or planning for all or part of the health system. Projects that use data collected by ICES under section 45 of PHIPA, and use no other data, are exempt from REB review. The use of the data in this project is authorized under section 45 and approved by ICES’ Privacy and Legal Office.

Background: Co-infections of SARS-CoV-2 with respiratory viruses, bacteria and fungi have been reported to cause a wide range of illness. Objectives: We assess the prevalence of co-infection of SARS-CoV-2 with seasonal respiratory viruses, document the respiratory viruses detected among individuals tested for SARS-CoV-2, and describe characteristics of individuals with respiratory virus co-infection detected. Methods: Specimens included in this study were submitted as part of routine clinical testing to Public Health Ontario Laboratory from individuals requiring testing for SARS-CoV-2 and/or seasonal respiratory viruses. Results: Co-infection was detected in a smaller proportion (2.5%) of individuals with laboratory confirmed SARS-CoV-2 than those with seasonal respiratory viruses (4.3%); this difference was not significant. Individuals with any respiratory virus co-infection were more likely to be younger than 65 years of age and male than those with single respiratory virus infection. Those with SARS-CoV-2 co-infection manifested mostly mild respiratory symptoms. Conclusions: Findings of this study may not support routine testing for seasonal respiratory viruses among all individuals tested for SARS-CoV-2, as they were rare during the study period nor associated with severe disease. However, testing for seasonal respiratory viruses should be performed in severely ill individuals, in which detection of other respiratory viruses may assist with patient management.

IntroductionWorkplaces requiring in-person attendance of employees for ongoing operations may be susceptible to SARS-CoV-2 outbreaks that impact workers as well as their close contacts. To understand industry sectors impacted by workplace outbreaks in the first wave of the pandemic, and the additional burden of illness through household transmission, we analyzed public health declared workplace outbreaks between January 21 to June 30, 2020, and their associated cases from January 21 to July 28.MethodsNumber, size and duration of outbreaks were described by sector, and outbreak cases were compared to sporadic cases in the same time frame. Address matching identified household cases with onset ≥2 days before, ≥2 days after, or within 1 day of the workplace outbreak case.ResultsThere were 199 outbreaks with 1245 cases, and 68% of outbreaks and 80% of cases belonged to i) Manufacturing, ii) Agriculture, Forestry, Fishing, Hunting, iii) Transportation and Warehousing. Median size of outbreaks was 3 cases (range: 1-140), and lasted median 7days (range: 0-119). Outbreak cases were significantly more likely to be male, younger, healthier, and have better outcomes. There were 608 household cases associated with 339 (31%) outbreak cases with valid addresses, increasing the burden of illness by 56%. The majority of household cases (368, 60%) occurred after the outbreak case.ConclusionsWorkplace outbreaks primarily occurred in three sectors. COVID-19 prevention measures should target industry sectors at risk by preventing introduction from exposed employees, spread in the workplace, and spread outside of the workplace.What is already known about this topic?COVID-19 outbreaks occur within workplaces and can spread to the communityWhat is added by this report?From January 21 – June 30, 2020, there were 199 workplace outbreaks in Ontario, Canada; 68% of outbreaks and 80% of outbreak-associated COVID-19 case were in three industry sectors: Manufacturing, Agriculture/Forestry/Fishing/Hunting, and Transportation/Warehousing. Household transmission occurred among 31% of outbreak cases, resulting in a 56% increase in workplace outbreak-associated cases when burden of household transmission is considered.What are the implications for public health practice?Workplace outbreak prevention measures should be targeted to industry sectors at risk by preventing introduction from exposed employees, spread in the workplace, and transmission to the greater community.

Introduction - Worldwide, nursing home residents have experienced disproportionately high COVID-19 mortality due to the intersection of congregate living, multimorbidity, and advanced age. Among 12 OECD countries, Canada has had the highest proportion of COVID-19 deaths in nursing home residents (78%), raising concerns about a skewed pandemic response that averted much transmission and mortality in community-dwelling residents, but did not adequately protect those in nursing homes. To investigate this, we measured temporal variations in hospitalizations among community and nursing home-dwelling decedents with COVID-19 during the first and second waves of the pandemic.Methods - We conducted a population-based cohort study of residents of Ontario, Canada with COVID-19 who died between March 11, 2020 (first COVID-19 death in Ontario) and October 28, 2020. We examined hospitalization prior to death as a function of 4 factors: community (defined as all non-nursing home residents) vs. nursing home residence, age in years (Results - A total of 3,114 people with confirmed COVID-19 died in Ontario from March to October, 2020 (Table 1), of whom 1,354 (43.5%) were hospitalized prior to death (median: 9 days before death, interquartile range: 4-19). Among nursing home decedents (N=2000), 22.4% were admitted to hospital prior to death, but this varied substantially from a low of 15.5% in March-April (peak of wave 1) to a high of 41.2% in June-July (nadir of wave 1). Among community-dwelling decedents (N=1,114), admission to acute care was higher (81.4%) and remained relatively stable throughout the first and second waves. Similar temporal trends for nursing home versus community decedents were apparent in age-stratified analyses (Figure 1). Women who died were less likely to have been hospitalized compared to men in both community (80% women vs 84% men) and nursing home (21% women vs 24% men) settings.Discussion - Only a minority of Ontario nursing home residents who died of COVID-19 were hospitalized prior to death, and that there were substantial temporal variations, with hospitalizations reaching their lowest point when overall COVID-19 incidence peaked in mid-April, 2020. While many nursing home residents had pre-pandemic advance directives precluding hospitalization, the low admission rate observed in March-April 2020 (15.5%) was inconsistent with both higher admission rates in subsequent months (>30%), and comparatively stable rates among community-dwelling adults. Our findings substantiate reports suggesting that hospitalizations for nursing home residents with COVID-19 were low during the peak of the pandemic’s first wave in Canada, which may have contributed to the particularly high concentration of COVID-19 mortality in Ontario’s nursing homes.

ImportanceProtecting healthcare workers (HCWs) from COVID-19 is a priority to maintain a safe and functioning healthcare system. The risk of transmitting COVID-19 to family members is a source of stress for many.ObjectiveTo describe and compare HCW and non-HCW COVID-19 cases in Ontario, Canada, as well as the frequency of COVID-19 among HCWs’ household members.Design, Setting, and ParticipantsUsing reportable disease data at Public Health Ontario which captures all COVID-19 cases in Ontario, Canada, we conducted a population-based cross-sectional study comparing demographic, exposure, and clinical variables between HCWs and non-HCWs with COVID-19 as of 14 May 2020. We calculated rates of infections over time and determined the frequency of within household transmissions using natural language processing based on residential address.Exposures and OutcomesWe contrasted age, gender, comorbidities, clinical presentation (including asymptomatic and presymptomatic), exposure histories including nosocomial transmission, and clinical outcomes between HCWs and non-HCWs with confirmed COVID-19.ResultsThere were 4,230 (17.5%) HCW COVID-19 cases in Ontario, of whom 20.2% were nurses, 2.3% were physicians, and the remaining 77.4% other specialties. HCWs were more likely to be between 30-60 years of age and female. HCWs were more likely to present asymptomatically (8.1% versus 7.0%, p=0.010) or with atypical symptoms (17.8% versus 10.5%, pConclusions and RelevanceHCWs represent a disproportionate number of COVID-19 cases in Ontario but with low confirmed numbers of nosocomial transmission. The data support substantial testing bias and under-ascertainment of general population cases. Protecting HCWs through appropriate personal protective equipment and physical distancing from colleagues is paramount.Key PointsQuestionWhat are the differences between healthcare workers and non-healthcare workers with COVID-19?FindingsIn this population-based cross-sectional study there were 4,230 healthcare workers comprising 17.5% of COVID-19 cases. Healthcare workers were diagnosed with COVID-19 at a rate 5.5 times higher than the general population with 0.8% of all healthcare workers, compared to 0.1% of non-healthcare workers.MeaningHigh healthcare worker COVID-19 burden highlights the importance of physical distancing from colleagues, appropriate personal protective equipment, as well as likely substantial testing bias and under-ascertainment of COVID-19 in the general population.

Introduction: Invasive pneumococcal disease (IPD) is a disease of public health significance in Ontario, Canada, where publicly funded pneumococcal vaccination programs target children, older adults, and people at high risk of disease. Since the implementation of pneumococcal conjugate vaccines (PCV), serotype replacement has been documented, where non-PCV serotypes replace the niche created by the reduction in vaccine-preventable serotypes. Our objective was to determine whether there has been serotype replacement or a change in IPD severity in Ontario since implementation of the childhood 13-valent (PCV13) program by assessing IPD burden over a 12-year period (2007-2018). Methods: We included all confirmed IPD cases reported in Ontario’s integrated Public Health Information System (iPHIS) and defined the pre-PCV13 era (January 2007-December 2010) and post-PCV13 era (January 2011-December 2018). We grouped IPD serotypes according to associated vaccine type: PCV13; 23-valent polysaccharide vaccine (unique PPV23); and non-vaccine-preventable (NVP). We used population data to calculate incidence and hospitalization rates (per 100,000 population) by age group, vaccine type, and era. Results: In the post-PCV13 era, PCV13-specific incidence and hospitalization rates decreased, while the incidence and hospitalizations due to unique PPV23 and NVP serotypes increased; this was consistent across all age groups. The greatest decrease in incidence (RR=0.4) and hospitalizations (RR=0.4) was observed in children

Introduction Annual influenza vaccination is recommended for older adults, but evidence regarding the impact of repeated vaccination has been inconclusive. Aim We investigated vaccine effectiveness (VE) against laboratory-confirmed influenza and the impact of repeated vaccination over 10 previous seasons on current season VE among older adults. Methods We conducted an observational test-negative study in community-dwelling adults aged > 65 years in Ontario, Canada for the 2010/11 to 2015/16 seasons by linking laboratory and health administrative data. We estimated VE using multivariable logistic regression. We assessed the impact of repeated vaccination by stratifying by previous vaccination history. Results We included 58,304 testing episodes for respiratory viruses, with 11,496 (20%) testing positive for influenza and 31,004 (53%) vaccinated. Adjusted VE against laboratory-confirmed influenza for the six seasons combined was 21% (95% confidence interval (CI): 18 to 24%). Patients who were vaccinated in the current season, but had received no vaccinations in the previous 10 seasons, had higher current season VE (34%; 95%CI: 9 to 52%) than patients who had received 1–3 (26%; 95%CI: 13 to 37%), 4–6 (24%; 95%CI: 15 to 33%), 7–8 (13%; 95%CI: 2 to 22%), or 9–10 (7%; 95%CI: −4 to 16%) vaccinations (trend test p = 0.001). All estimates were higher after correcting for misclassification of current season vaccination status. For patients who were not vaccinated in the current season, residual protection rose significantly with increasing numbers of vaccinations received previously. Conclusions Although VE appeared to decrease with increasing numbers of previous vaccinations, current season vaccination likely provides some protection against influenza regardless of the number of vaccinations received over the previous 10 influenza seasons.

Purpose The aim of the present study was to quantify associations between sexualized drug use (SDU) and sexually-transmitted and blood-borne infection (STBBI) diagnoses in gay, bisexual and other men who have sex with men (GBMSM) with defined temporal proximity between SDU exposure and STBBI diagnoses. Methods In May 2018 and June 2019, we searched the literature for primary studies that quantified the association between STBBI and SDU among GBMSM. A random-effects model was used to meta-analyze the data and estimate the association between SDU and STBBIs. Results Nineteen studies met the inclusion criteria and fourteen studies were included in the meta-analyses. SDU was associated with higher odds of bacterial STI diagnoses, higher odds of HCV diagnoses, and higher odds of HIV diagnoses. Associations between SDU and diagnoses of bacterial STIs or HCV remained after adjustment for behavioral and sociodemographic factors. Conclusions Robust and consistent associations between SDU and STBBI identified in this review add to the evidence suggesting SDU is a potential contributor to bacterial STIs and HCV or a proxy indicator for other risk factors.

Importance As a result of low numbers of pediatric cases early in the COVID-19 pandemic, pediatric household transmission of SARS-CoV-2 remains an understudied topic. Objective To determine whether there are differences in the odds of household transmission by younger children compared with older children. Design, Setting, and Participants This population-based cohort study took place between June 1 and December 31, 2020, in Ontario, Canada. Private households in which the index case individual of laboratory-confirmed SARS-CoV-2 infection was younger than 18 years were included. Individuals were excluded if they resided in apartments missing suite information, in households with multiple index cases, or in households where the age of the index case individual was missing. Exposures Age group of pediatric index cases categorized as 0 to 3, 4 to 8, 9 to 13, and 14 to 17 years. Main Outcomes and Measures Household transmission, defined as households where at least 1 secondary case occurred 1 to 14 days after the pediatric index case. Results A total of 6280 households had pediatric index cases, and 1717 households (27.3%) experienced secondary transmission. The mean (SD) age of pediatric index case individuals was 10.7 (5.1) years and 2863 (45.6%) were female individuals. Children aged 0 to 3 years had the highest odds of transmitting SARS-CoV-2 to household contacts compared with children aged 14 to 17 years (odds ratio, 1.43; 95% CI, 1.17-1.75). This association was similarly observed in sensitivity analyses defining secondary cases as 2 to 14 days or 4 to 14 days after the index case and stratified analyses by presence of symptoms, association with a school/childcare outbreak, or school/childcare reopening. Children aged 4 to 8 years and 9 to 13 years also had increased odds of transmission (aged 4-8 years: odds ratio, 1.40; 95% CI, 1.18-1.67; aged 9-13 years: odds ratio, 1.13; 95% CI, 0.97-1.32). Conclusions and Relevance This study suggests that younger children may be more likely to transmit SARS-CoV-2 infection compared with older children, and the highest odds of transmission was observed for children aged 0 to 3 years. Differential infectivity of pediatric age groups has implications for infection prevention within households, as well as schools/childcare, to minimize risk of household secondary transmission. Additional population-based studies are required to establish the risk of transmission by younger pediatric index cases.

Background In September 2009, a live attenuated herpes zoster vaccine (ZVL) became available in Canada. Beginning in September 2016, ZVL was made available to all Ontario residents aged 65–70 through a publicly funded immunization program. We assessed the impact of ZVL availability and its subsequent public funding on herpes zoster burden in this population. Methods A population-based study of Ontario residents aged 65–70 between January 2005 and September 2018. We used interventional autoregressive integrated moving average models to examine the impact of ZVL market availability and the publicly funded ZVL program on monthly incidence rate of medically attended herpes zoster, defined as an outpatient visit for herpes zoster with a prescription for a herpes zoster antiviral dispensed ≤5 days before or after the visit, or a herpes zoster–related emergency department (ED) visit or hospitalization. In secondary analyses, we examined impacts on any herpes zoster–related ED visits and hospitalizations. Results We found no association between ZVL market availability and monthly incidence of herpes zoster (P = .32) or monthly rates of ED visits and hospitalizations (P = .88). Conversely, the introduction of publicly funded ZVL reduced the monthly rate of medically attended herpes zoster by 19.1% (from 4.8 to 3.8 per 10 000 population; P, In this population-based study, introduction of a publicly funded herpes zoster vaccination program for all adults aged 65–70 reduced the burden of medically attended herpes zoster and herpes zoster–related emergency department visits and hospitalizations at a population level.

Background Immunocompromised adults are at .increased risk of herpes zoster (HZ) infection and related complications. We aimed to assess the incidence of hospital-attended HZ (ie, seen in hospital or emergency department) in immunocompromised populations and compare it to immunocompetent populations. Methods We calculated incidence rates (IRs) of hospital-attended HZ in Ontario, Canada, between 1 April 2002 and 31 August 2016 in adults ≥18 years of age categorized as immunocompromised or immunocompetent. We repeated these analyses by type of immunocompromising condition and provided incidence rate ratios (IRRs) comparing to immunocompetent adults. We also calculated IRs and IRRs of HZ complications by immunocompromised status. Results There were 135 206 incident cases of hospital-attended HZ during the study period. Immunocompromised adults accounted for 13% of these cases despite representing 3% of the population. The risk of hospital-attended HZ was higher for immunocompromised adults compared with immunocompetent adults (IRR, 2.9 [95% confidence interval {CI}, 2.9–3.0]) and ranged across type of immunocompromising conditions, from 2.6 (95% CI, 2.6–2.7) in those with a solid tumor malignancy to 12.3 (95% CI, 11.3–13.2) in those who had undergone hematopoietic stem cell transplant. The risk of any HZ complication was higher in immunocompromised adults (IRR, 3.6 [95% CI, 3.5–3.7]) and highest for disseminated zoster (IRR, 32.8 [95% CI, 27.8–38.6]). Conclusions The risk of hospital-attended HZ and related complications was higher in immunocompromised populations compared with immunocompetent populations. Our findings underscore the high-risk nature of this population and the potential benefits that may be realized through HZ vaccination.

Background Respiratory illnesses are a major contributor to pediatric hospitalizations, with influenza and respiratory syncytial virus (RSV) causing substantial morbidity and cost each season. We compared the characteristics and outcomes of children 0-59 months of age who were hospitalized with laboratory-confirmed influenza or RSV between 2009 and 2014 in Ontario, Canada. Methods We included hospitalized children who were tested for influenza A, influenza B and RSV and were positive for a single virus. We characterized individuals by their demographics and healthcare utilization patterns and compared their hospital outcomes, in-hospital cost and postdischarge healthcare use by virus type and by presence of underlying comorbidities. Results We identified and analyzed 7659 hospitalizations during which a specimen tested positive for influenza or RSV. Children with RSV were the youngest whereas children with influenza B were the oldest [median ages 6 months (interquartile range: 2-17 months) and 25 months (interquartile range: 10-45 months), respectively]. Complex chronic conditions were more prevalent among children with all influenza (sub)types than RSV (31%-34% versus 20%). In-hospital outcomes were similar by virus type, but in children with comorbidities, postdischarge outcomes varied. We observed no differences in in-hospital cost between viruses or by presence of comorbidities [overall median cost: $4150 Canadian dollars (interquartile range: $3710-$4948)]. Conclusions Influenza and RSV account for large numbers of pediatric hospitalizations. RSV and influenza were similar in terms of severity and cost in hospitalized children. Influenza vaccination should be promoted in pregnant women and young children, and a vaccine against RSV would mitigate the high burden of RSV.

Introduction Protecting healthcare workers (HCWs) from Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) is a priority to maintain a safe and functioning healthcare system. Our objective was to describe and compare the epidemiology, clinical characteristics, and lethality of SARS-CoV-2 infections among HCWs compared to non-HCWs. Methods Using reportable disease data at Public Health Ontario, we conducted a population-based cross-sectional study comparing demographic, exposure, and clinical variables between HCWs and non-HCWs with SARS-CoV-2 infections as of 30 September 2020. We calculated rates of infections over time and determined the frequency of within household transmissions using natural language processing based on residential address. We evaluated the risk of death using a multivariable logistic regression model adjusting for age, sex, comorbidities, symptoms, and long-term care home exposure. Results There were 7,050 (12.5%) HCW SARS-CoV-2 infections in Ontario, Canada, of whom 24.9% were nurses, 2.3% were physicians, and the remaining 72.8% other specialties, including personal support workers. Overall HCWs had an infection rate of 1,276 per 100,000 compared to non-HCWs of 346 per 100,000 (3.7 times higher). This difference decreased from a 7 times higher rate in April to no difference in September 2020. Twenty-six percent of HCWs had a household member with SARS-CoV-2 infection; 6.8% were probable acquisitions, 12.3% secondary transmissions, and 6.9% unknown direction of transmission. Death among HCWs was 0.2% compared to 6.1% of non-HCWs. The risk of death in HCWs remained significantly lower than non-HCWs after adjustment (adjusted odds ratio 0.09; 95%CI 0.05–0.17). Conclusion HCWs represent a disproportionate number of diagnosed SARS-CoV-2 infections in Ontario, however this discrepancy is at least partially explained by limitations in testing earlier in the pandemic for non-HCWs. We observed a low risk of death in HCWs which could not be completely explained by other factors.

Aim The burden of disease in children attributable to influenza viruses is difficult to quantify given the similarity of symptoms caused by infection due to influenza and other viruses. This uncertainty impacts clinical decision-making and estimates of burden. We aimed to systematically review the literature to determine the proportion of healthy children presenting for health care with an acute respiratory illness (ARI) who have laboratory-confirmed seasonal influenza (PROSPERO ID#CRD42014013896). Method We searched Ovid MEDLINE, EMBASE, Scopus, and references of included articles. We included studies that used polymerase chain reaction methods to test for influenza in healthy children aged ≤5 years who presented for health care in high-income countries with an influenza-like or ARI. A standardized form was used to collect data on positivity and other relevant study elements. Results Seventeen studies covering 12 different influenza seasons were included. The proportion of influenza positivity ranged from 11% to 56%. Subgroup analyses were performed by influenza season, continent, healthcare setting, age group, and vaccination status. Higher influenza positivity was reported among children aged 3-5 years compared with children aged ≤2 years, and for unvaccinated children. Conclusion The minority of healthy patients aged ≤5 years with medically attended influenza-like or acute respiratory symptoms have laboratory-confirmed influenza virus infection, although this varied by influenza season. Prevention efforts should be targeted accordingly. Statement Most influenza-like illnesses are not laboratory-confirmed and have similar clinical presentations. Consequently, the true contribution of influenza to acute respiratory infections in children remains uncertain. Our systematic review estimates that this proportion ranges from 11% to 56%. This finding can help both clinicians and public health professionals target prevention.

BACKGROUND: Uptake of influenza vaccination in Canada remains suboptimal despite widespread public funding. To increase access, several provinces have implemented policies permitting pharmacists to administer influenza vaccines in community pharmacies. We examined the impact of such policies on the uptake of seasonal influenza vaccination in Canada. METHODS: We pooled data from the 2007–2014 cycles of the Canadian Community Health Survey (n = 481 526). To determine the impact of influenza vaccine administration by pharmacists, we estimated the prevalence ratio for the association between the presence of a pharmacist policy and individual-level vaccine uptake using a modified Poisson regression model (dependent variable: vaccine uptake) with normalized weights while controlling for numerous health and sociodemographic factors. RESULTS: Across all survey cycles combined, 28.8% of respondents reported receiving a seasonal influenza vaccine during the 12 months before survey participation. Introduction of a policy for pharmacist administration of influenza vaccine was associated with a modest increase in coverage (2.2%) and an individual’s likelihood of uptake (adjusted prevalence ratio 1.05, 95% confidence interval 1.02–1.08). INTERPRETATION: Uptake of influenza immunization was modestly increased in Canadian jurisdictions that allowed pharmacists to administer influenza vaccines.

The authors have retracted this article, The impact of repeated vaccination on influenza vaccine effectiveness: a systematic review and meta-analysis.

IntroductionAnnual evaluation of influenza vaccine effectiveness (VE) is required because of frequent changes to circulating and vaccine strains. Traditionally, VE studies enroll patients who fulfill case definitions for respiratory infections and are tested for influenza. VE estimates generated from convenience samples of routinely collected specimens might be biased. Objectives and ApproachWe assessed the validity of using data from respiratory specimens collected during clinical encounters to estimate VE. We created the Flu and Other Respiratory Viruses Research (FOREVER) Cohort by linking respiratory virus laboratory test results from 2009-2014 from 11 public health and 8 hospital laboratories across Ontario to health administrative databases, including databases with billing claims for physician- and pharmacist-administered influenza vaccines. We evaluated the presence of information and selection biases when using these data and estimated VE in community-dwelling older adults (>65) using the test-negative design under conditions that emulated the inclusion criteria in traditional VE studies. ResultsThe FOREVER Cohort included test results from 283,711 respiratory specimens obtained from 216,730 individuals. The overall linkage proportion to health administrative databases using deterministic and probabilistic linkage methods was 97.5%. Influenza positivity for older adults with unknown lag between illness onset and specimen collection was similar to those for whom illness onset date was documented to be ≤7 days before specimen collection, suggesting minimal outcome misclassification associated with information bias. The likelihood of influenza testing was similar between vaccinated and unvaccinated individuals, suggesting an absence of selection bias that could arise when a case definition for influenza testing is not employed. Lastly, VE estimates were similar under various conditions, demonstrating the robustness of using these data, and were comparable to published estimates. Conclusion/ImplicationsThe FOREVER Cohort can be used to estimate VE with negligible bias. Compared to traditional VE studies that are limited to recruited patients, routinely collected specimens create a larger, more generalizable sample. Linkage to health administrative databases can identify those with comorbidities and permit evaluation of VE in high-risk groups.

Importance Recent observational studies report conflicting results regarding the effectiveness of live attenuated influenza vaccine (LAIV), particularly against influenza A(H1N1)pdm09. Objective To compare the effectiveness of LAIV and inactivated influenza vaccine (IIV) against laboratory-confirmed influenza. Design, Setting, and Participants A test-negative study to estimate influenza vaccine effectiveness (VE) using population-based, linked, individual-level laboratory, health administrative, and immunization data. Data were obtained from 10 169 children and adolescents aged 2 to 17 years (children) who were tested for influenza in inpatient or outpatient settings during periods when influenza was circulating based on a threshold level of 5% weekly test positivity for the province during the 4 influenza seasons spanning from November 11, 2012, to April 30, 2016, in Alberta, Canada. Logistic regression was used to estimate VE by vaccine type, influenza season, and influenza type and subtype. The relative effectiveness of each vaccine type was assessed by comparing the odds of laboratory-confirmed influenza infection for LAIV recipients with that for IIV recipients. Exposures The primary exposure was receipt of LAIV or IIV before testing for influenza. Main Outcomes and Measures The primary outcome was influenza case status as determined by reverse-transcriptase polymerase chain reaction testing. Results A total of 10 779 respiratory specimens (from 10 169 children) collected and tested for influenza during the 4 influenza seasons were included, with 53.4% from males; the mean (SD) age was 7.0 (4.6) years. Across the 4 influenza seasons, 3161 children tested positive for influenza. Combining the 4 influenza seasons, the adjusted VE against influenza A(H1N1)pdm09 was 69% (95% CI, 56%-78%) for LAIV compared with 79% (95% CI, 70%-86%) for IIV. Vaccine effectiveness against influenza A(H3N2) was 36% (95% CI, 14%-53%) for LAIV and 43% (95% CI, 22%-59%) for IIV. Against influenza B, VE was 74% (95% CI, 62%-82%) for LAIV and 56% (95% CI, 41%-66%) for IIV. There were no significant differences in the odds of influenza infection for LAIV recipients compared with IIV recipients except for influenza B during the 2015-2016 season, when LAIV recipients had lower odds of infection than IIV recipients (odds ratio, 0.36; 95% CI, 0.17-0.76). Conclusions and Relevance There was no evidence to support the lack of effectiveness of LAIV against influenza A(H1N1)pdm09. These results support administration of either vaccine type in this age group.

Few studies have addressed respiratory syncytial virus (RSV) infection during pregnancy. Among 846 pregnant women hospitalized with respiratory illness and tested for RSV, 21 (2%) were RSV positive, of whom 8 (38%) were diagnosed with pneumonia. Despite study limitations, these data can help inform decisions about RSV prevention strategies.

Background Conflicting results regarding the impact of repeated vaccination on influenza vaccine effectiveness (VE) may cause confusion regarding the benefits of receiving the current season’s vaccine. Methods We systematically searched MEDLINE, Embase, PubMed, and Cumulative Index to Nursing and Allied Health Literature from database inception to August 17, 2016, for observational studies published in English that reported VE against laboratory-confirmed influenza for the following four vaccination groups: current season only, prior season only, both seasons, and neither season. We pooled differences in VE (∆VE) between vaccination groups by influenza season and type/subtype using a random-effects model. The study protocol is registered with PROSPERO (registration number: CRD42016037241). Results We identified 3435 unique articles, reviewed the full text of 634, and included 20 for meta-analysis. Compared to prior season vaccination only, vaccination in both seasons was associated with greater protection against influenza H1N1 (∆VE = 25%; 95% CI 14%, 35%) and B (∆VE = 18%; 95% CI 3%, 33%), but not H3N2 (∆VE = 7%; 95% CI – 7%, 21%). Compared to no vaccination for either season, individuals who received the current season’s vaccine had greater protection against H1N1 (∆VE = 62%; 95% CI 51%, 70%), H3N2 (∆VE = 45%; 95% CI 35%, 53%), and B (∆VE = 64%; 95% CI 57%, 71%). We observed no differences in VE between vaccination in both seasons and the current season only for H1N1 (∆VE = 3%; 95% CI – 8%, 13%), but less protection against influenza H3N2 (∆VE = − 20%; 95% CI – 36%, − 4%), and B (∆VE = − 11%; 95% CI – 20%, − 2%). Conclusions Our results support current season vaccination regardless of prior season vaccination because VE for vaccination in the current season only is higher compared to no vaccination in either season for all types/subtypes, and for H1N1 and influenza B, vaccination in both seasons provides better VE than vaccination in the prior season only. Although VE was lower against H3N2 and B for individuals vaccinated in both seasons compared to those vaccinated in the current season only, it should be noted that past vaccination history cannot be altered and this comparison disregards susceptibility to influenza during the prior season among those vaccinated in the current season only. In addition, our results for H3N2 were particularly influenced by the 2014–2015 influenza season and the impact of repeated vaccination for all types/subtypes may vary from season to season. It is important that future VE studies include vaccination history over multiple seasons to evaluate repeated vaccination in more detail. Electronic supplementary material The online version of this article (10.1186/s12916-018-1239-8) contains supplementary material, which is available to authorized users.

Uncertainty remains regarding the magnitude of effectiveness of influenza vaccines for preventing serious outcomes, especially among young children. We estimated vaccine effectiveness (VE) against laboratory-confirmed influenza hospitalizations among children aged 6–59 months. We used the test-negative design in hospitalized children in Ontario, Canada during the 2010–11 to 2013–14 influenza seasons. We used logistic regression models adjusted for age, season, and time within season to calculate VE estimates by vaccination status (full vs. partial), age group, and influenza season. We also assessed VE incorporating prior history of influenza vaccination. We included specimens from 9,982 patient hospitalization episodes over four seasons, with 12.8% testing positive for influenza. We observed variation in VE by vaccination status, age group, and influenza season. For the four seasons combined, VE was 60% (95%CI, 44%-72%) for full vaccination and 39% (95%CI, 17%-56%) for partial vaccination. VE for full vaccination was 67% (95%CI, 48%-79%) for children aged 24–59 months, 48% (95%CI, 12%-69%) for children aged 6–23 months, 77% (95%CI, 47%-90%) for 2010–11, 59% (95%CI, 13%-81%) for 2011–12, 33% (95%CI, –18% to 62%) for 2012–13, and 72% (95%CI, 42%-86%) for 2013–14. VE in children aged 24–59 months appeared similar between those vaccinated in both the current and previous seasons and those vaccinated in the current season only, with the exception of 2012–13, when VE was lower for those vaccinated in the current season only. Influenza vaccination is effective in preventing pediatric laboratory-confirmed influenza hospitalizations during most seasons.

IntroductionThe appropriateness of using routinely collected laboratory data combined with administrative data for estimating influenza vaccine effectiveness (VE) is still being explored. This paper outlines a protocol to estimate influenza VE using linked laboratory and administrative data which could act as a companion to estimates derived from other methods.Methods and analysisWe will use the test-negative design to estimate VE for each influenza type/subtype and season. Province-wide individual-level records of positive and negative influenza tests at the Provincial Laboratory for Public Health in Alberta will be linked, by unique personal health numbers, to administrative databases and vaccination records held at the Ministry of Health in Alberta to determine covariates and influenza vaccination status, respectively. Covariates of interests include age, sex, immunocompromising chronic conditions and healthcare setting. Cases will be defined based on an individual’s first positive influenza test during the season, and potential controls will be defined based on an individual’s first negative influenza test during the season. One control for each case will be randomly selected based on the week the specimen was collected. We will estimate VE using multivariable logistic regression.Ethics and disseminationEthics approval was obtained from the University of Alberta’s Health Research Ethics Board—Health Panel under study ID Pro00075997. Results will be disseminated by public health officials in Alberta.

BACKGROUND Influenza immunization coverage among Canadian health care personnel remains below national targets. Targeting this group is of particular importance given their elevated risk of influenza infection, role in transmission and influence on patients' immunization status. We examined influenza immunization coverage in health care personnel in Canada, reasons for not being immunized and the impact of "vaccinate-or-mask" influenza prevention policies. METHODS In this national cross-sectional study, we pooled data from the 2007 to 2014 cycles of the Canadian Community Health Survey and restricted it to respondents who reported a health care occupation. Using bootstrapped survey weights, we examined immunization coverage by occupation and by presence of vaccinate-or-mask policies, and reasons for not being immunized. We used modified Poisson regression to estimate the prevalence ratio (PR) of influenza immunization for health care occupations compared with the general working population. RESULTS For all survey cycles combined, 50% of 18 446 health care personnel reported receiving seasonal influenza immunization during the previous 12 months, although this varied by occupation type (range 4%-72%). Compared with the general working population, family physicians and general practitioners were most likely to be immunized (PR 3.15, 95% confidence interval [CI] 2.76-3.59), whereas chiropractors, midwives and practitioners of natural healing were least likely (PR 0.17, 95% CI 0.10-0.30). Among those who were not immunized, the most frequently cited reason was the belief that influenza immunization is unnecessary. Introduction of vaccinate-or-mask policies was associated with increased influenza immunization among health care personnel. INTERPRETATION Health care personnel are more likely to be immunized against influenza than the general working population, but coverage remains suboptimal overall, and we observed wide variation by occupation type. More efforts are needed to target specific health care occupations with low immunization coverage.