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Objective To examine the association between maternal mRNA covid-19 vaccination during the first trimester of pregnancy and the prevalence of major congenital anomalies in offspring.Design Population based cohort study with sibling matched analysis.Setting Multiple health administrative databases, linked and analysed at ICES, an independent, non-profit research institute that collects and analyses healthcare and demographic data, Ontario, Canada, from 16 October 2021 to 1 May 2023.Population 174 296 singleton live births >20 weeks' gestation with an expected birth date between 16 October 2021 and 1 May 2023: 34 181 (20%) born to mothers who received one or two doses of an mRNA covid-19 vaccine in the first trimester and 34 951 (20%) born to mothers who did not receive a vaccine before or during pregnancy. The sibling matched analysis included 13 312 infants exposed to a covid-19 vaccine in the first trimester and 15 089 matched older siblings with the same mother, with an expected birth date after 16 October 2016 and no reported in utero exposure to a covid-19 vaccine.Main outcome measures Major congenital anomalies, overall and grouped by specific organ systems, diagnosed within 28 days of birth.Results Major congenital anomalies were present in 832 (24.3 per 1000 live births) infants exposed to an mRNA covid-19 vaccine in the first trimester compared with 927 (26.5 per 1000 live births) infants not exposed to a vaccine, resulting in an adjusted prevalence ratio of 0.89 (95% confidence interval (CI) 0.79 to 1.01). Major congenital anomalies were present in 283 (21.3 per 1000 live births) and 343 (22.7 per 1000 live births) infants exposed to an mRNA covid-19 vaccine in the first trimester and their older siblings not exposed to a vaccine, respectively (adjusted prevalence ratio 0.91, 95% CI 0.77 to 1.07). First trimester vaccination was not associated with an increase in major congenital anomalies grouped by specific organ system in the primary or sibling matched analyses. Results were similar across a range of subgroup and sensitivity analyses.Conclusions In this large population based cohort study and sibling matched analysis, mRNA covid-19 vaccination during the first trimester of pregnancy was not associated with an increase in major congenital anomalies in offspring, overall or grouped by organ system.

Objective Health administrative data can support population-level research among people who inject drugs (PWID), however these data sources remain underutilized due to the difficulty in identifying drug use in routinely collected data. We validated case-ascertainment algorithms to identify PWID and tested their application in a hepatitis C (HCV) cohort in Ontario, Canada. Approach We conducted a validation study using reference standard cohorts of PWID recruited via community-based studies and population controls linked to health administrative data in Ontario, Canada (1992-2020). Tested case-ascertainment algorithms included combinations of hospitalizations/emergency department (ED) visits for drug use/poisoning, physician visits for drug use, opioid agonist treatment (OAT), or injecting-related infections. Sensitivity and specificity were estimated for lifetime history and recent injecting (past 1-5 years). We applied a high-performing algorithm among all Ontarians with laboratory-confirmed HCV between 1999-2018, to identify a sub-cohort of PWID with HCV. Results An algorithm including ≥1 hospitalization/ED visit or ≥1 physician visit for drug use or ≥1 OAT record had high accuracy for identifying IDU history (91.6% sensitivity, 94.2% specificity) and recent IDU (using 3 years lookback: 80.4% sensitivity, 99% specificity). When applied to a provincial cohort of 112,947 Ontarians diagnosed with HCV, this algorithm estimated 46% (N=52,248) had a history of IDU, of whom 52% (N=27,246) had an indication of recent IDU (within the past 3 years). Conclusion The methods developed in this study can enhance the capacity of population-level health research among people who inject drugs and support applied public health interventions towards hepatitis C elimination.

BackgroundSARS-CoV-2 variants of concern (VOCs) emerged and rapidly replaced the original strain worldwide. The increased transmissibility of these new variants led to increases in infections, hospitalizations, and mortality. However, there is a scarcity of retrospective investigations examining the severity of all the main VOCs in presence of key public health measures and within various social determinants of health (SDOHs). ObjectiveThis study aims to provide a retrospective assessment of the clinical severity of COVID-19 VOCs in the context of heterogenous SDOHs and vaccination rollout. MethodsWe used a population-based retrospective cohort design with data from the British Columbia COVID-19 Cohort, a linked provincial surveillance platform. To assess the relative severity (hospitalizations, intensive care unit [ICU] admissions, and deaths) of Gamma, Delta, and Omicron infections during 2021 relative to Alpha, we used inverse probability treatment weighted Cox proportional hazard modeling. We also conducted a subanalysis among unvaccinated individuals, as assessed severity differed across VOCs and SDOHs. ResultsWe included 91,964 individuals infected with a SARS-CoV-2 VOC (Alpha: n=20,487, 22.28%; Gamma: n=15,223, 16.55%; Delta: n=49,161, 53.46%; and Omicron: n=7093, 7.71%). Delta was associated with the most severe disease in terms of hospitalization, ICU admissions, and deaths (hospitalization: adjusted hazard ratio [aHR] 2.00, 95% CI 1.92-2.08; ICU: aHR 2.05, 95% CI 1.91-2.20; death: aHR 3.70, 95% CI 3.23-4.25 relative to Alpha), followed generally by Gamma and then Omicron and Alpha. The relative severity by VOC remained similar in the unvaccinated individual subanalysis, although the proportion of individuals infected with Delta and Omicron who were hospitalized was 2 times higher in those unvaccinated than in those fully vaccinated. Regarding SDOHs, the proportion of hospitalized individuals was higher in areas with lower income across all VOCs, whereas among Alpha and Gamma infections, 2 VOCs that cocirculated, differential distributions of hospitalizations were found among racially minoritized groups. ConclusionsOur study provides robust severity estimates for all VOCs during the COVID-19 pandemic in British Columbia, Canada. Relative to Alpha, we found Delta to be the most severe, followed by Gamma and Omicron. This study highlights the importance of targeted testing and sequencing to ensure timely detection and accurate estimation of severity in emerging variants. It further sheds light on the importance of vaccination coverage and SDOHs in the context of pandemic preparedness to support the prioritization of allocation for resource-constrained or minoritized groups.

BackgroundEvidence on protection of different patterns of infection- and vaccine-acquired immunity against Omicron-associated severe illness is useful in planning booster vaccination strategies. We examined protection of prior SARS-CoV-2 infection, a third or a fourth COVID-19 vaccine dose, and hybrid immunity against Omicron-associated severe illness.Methods and findingsThis population-based cohort study followed five million individuals with at least one SARS-CoV-2 RT-PCR test before November 21, 2021 until an Omicron-associatedhospitalization or death. We used Cox regression models to estimate risks of Omicron-associated hospitalization and a composite severe outcome (hospitalized and death), among individuals with infection- and/or vaccination-acquired immunity. Individuals who were unvaccinated and had no history of a prior infection severed as the reference group. Both adjusted hazard ratios (HR) and corresponding protection (one minus adjusted HR), with 95% confidence intervals (CIs), were reported. Three doses provided 94% (95%CI 93-95) and 93% (95%CI 91-94) protection against Omicron-associated hospitalization at 2-3 and ≥3 months post-vaccination respectively, similar to the protection conferred by three doses and a prior infection (2-3 months: 99%, 95%CI 97-100; ≥3 months: 97%, 95%CI 92-99) and four doses (1 month: 87%, 95%CI 79-92; 1-2 months: 96%, 95%CI 92-98). In individuals ≥65 years old, protection of four doses increased to 95% (95%CI 91-98) at 1-2 months, significantly higher than that of three doses over the follow-up period. Similar results were observed with the composite severe outcome.ConclusionAt least three antigenic exposures, achieved by vaccination or infection, confers significant protection against Omicron-associated hospitalization and death in all age groups. Our findings support a third dose for the overall population, regardless of prior infection status, and a fourth dose for the elderly to maintain high level of immunity and substantially reduce risk of severe illness at individual level.

Abstract Background Regional variations in SARS-CoV-2 infection were observed in Canada and other countries. Studies have used multilevel analyses to examine how a context, such as a neighbourhood, can affect the SARS-CoV-2 infection rates of the people within it. However, few multilevel studies have quantified the magnitude of the general contextual effect (GCE) in SARS-CoV-2 infection rates and assessed how it may be associated with individual- and area-level characteristics. To address this gap, we will illustrate the application of the median rate ratio (MRR) in a multilevel Poisson analysis for quantifying the GCE in SARS-CoV-2 infection rates in Ontario, Canada. Methods We conducted a population-based, two-level multilevel observational study where individuals were nested into regions (i.e., forward sortation areas [FSAs]). The study population included community-dwelling adults in Ontario, Canada, between March 1, 2020, and May 1, 2021. The model included seven individual-level variables (age, sex, asthma, diabetes, hypertension, congestive heart failure, and chronic obstructive pulmonary disease) and four FSA census-based variables (household size, household income, employment, and driving to work). The MRR is a median value of the rate ratios comparing two patients with identical characteristics randomly selected from two different regions ordered by rate. We examined the attenuation of the MRR after including individual-level and FSA census-based variables to assess their role in explaining the variation in rates between regions. Results Of the 11 789 128 Ontario adult community-dwelling residents, 343 787 had at least one SARS-CoV-2 infection during the study period. After adjusting for individual-level and FSA census-based variables, the MRR was attenuated to 1.67 (39% reduction from unadjusted MRR). The strongest FSA census-based associations were household size (RR = 1.88, 95% CI: 1.71–1.97) and driving to work (RR = 0.68, 95% CI: 0.65–0.71). Conclusions The individual- and area-level characteristics in our study accounted for approximately 40% of the between-region variation in SARS-CoV-2 infection rates measured by MRR in Ontario, Canada. These findings suggest that population-based policies to address social determinants of health that attenuate the MRR may reduce the observed between-region heterogeneity in SARS-CoV-2 infection rates.

Abstract Background and aims There is an incomplete understanding of the full safety profiles of repeated COVID-19 vaccinations in patients with inflammatory bowel disease (IBD). Among individuals with IBD, we assessed whether COVID-19 vaccines were associated with serious adverse events of special interest (AESI) and health care utilization [all-cause hospitalizations, Emergency Department (ED) visits, gastroenterology visits, IBD-related visits]. Methods Using comprehensive administrative health data from Ontario, Canada, adults with IBD who received at least one COVID-19 vaccine from December 2020-January 2022 were included. Self-controlled case series analyses were conducted to evaluate the relative incidence rates of AESI and health care utilization outcomes across post-vaccination risk and control periods. Results Among 88,407 IBD patients, 99.7% received mRNA vaccines and 75.9% received ≥ 3 doses. Relative to control periods, we did not detect an increase in AESI. IBD patients had fewer all-cause hospitalizations during post-vaccination risk periods. Patients experienced more all-cause ED visits after dose 2 [Relative Incidence (RI):1.08(95%CI:1.04–1.12)] but fewer visits after doses 3 [RI:0.85 (95%CI:0.81–0.90)] and 4 [RI:0.73 (95%CI:0.57–0.92)]. There was no increase in gastroenterologist visits or IBD-related health care utilization post-vaccination. There were fewer IBD-related hospitalizations after dose 1 [RI:0.84 (95%CI:0.72–0.98)] and 3 [RI:0.63 (95%CI:0.52–0.76)], fewer IBD-related ED visits after dose 3 [RI:0.81 (95%CI:0.71–0.91)] and 4 [RI:0.55 (95%CI:0.32–0.96)], and fewer outpatient visits after dose 2 [RI:0.91 (95%CI:0.90–0.93)] and 3 [RI:0.87 (95%CI:0.86–0.89)]. Conclusion This population-based study did not detect increased AESI, all-cause or IBD-related health care utilization following COVID-19 vaccination, suggesting a lack of association between vaccination and increased disease activity.

Objective: To compare myocarditis/pericarditis risk after COVID-19 mRNA vaccination versus SARS-CoV-2 infection, and to assess if myocarditis/pericarditis risk varies by vaccine dosing interval. Methods: In this retrospective cohort study, we used linked databases in Quebec, Ontario, and British Columbia between January 26, 2020, and September 9, 2021. We included individuals aged 12 or above who received an mRNA vaccine as the second dose or were SARS-CoV-2-positive by RT-PCR. The outcome was hospitalization/emergency department visit for myocarditis/pericarditis within 21 days of exposure. We calculated age- and sex-stratified incidence ratios (IRs) of myocarditis/pericarditis following mRNA vaccination versus SARS-CoV-2 infection. We also calculated myocarditis/pericarditis incidence by vaccine type, homologous/heterologous schedule, and dosing interval. We pooled province-specific estimates using meta-analysis. Results: Following 18,860,817 mRNA vaccinations and 860,335 SARS-CoV-2 infections, we observed 686 and 160 myocarditis/pericarditis cases, respectively. Myocarditis/pericarditis incidence was lower after vaccination than infection (IR [BNT162b2/SARS-CoV-2], 0.14; 95%CI, 0.07–0.29; IR [mRNA-1273/SARS-CoV-2], 0.28; 95%CI, 0.20–0.39). Within the vaccinated cohort, myocarditis/pericarditis incidence was lower with longer dosing intervals; IR (56 or more days/15–30 days) was 0.28 (95%CI, 0.19–0.41) for BNT162b2 and 0.26 (95%CI, 0.18–0.38) for mRNA-1273. Conclusion: Myocarditis/pericarditis risk was lower after mRNA vaccination than SARS-CoV-2 infection, and with longer intervals between primary vaccine doses.

Background: The World Health Organization (WHO) has set hepatitis C (HCV) elimination targets for 2030. Understanding existing gaps in the “HCV care-cascade” is essential for meeting these targets. We aimed to identify the level of service scale-up needed along the “HCV care-cascade” to achieve the WHO’s HCV elimination targets in Ontario, Canada. Methods: By employing a decision analytic model, we projected the quality-adjusted life years (QALYs) and healthcare costs for individuals with HCV in Ontario. We increased RNA testing and treatment rates to 98%, followed by increasing antibody testing uptake until we achieved the WHO’s mortality target (i.e., a 65% reduction in liver-related mortality by 2030 vs. 2015). Results: Without scaling up by 2030, the expected QALYs and costs per person were 9.156 and CAD 48,996, respectively. Improved RNA testing and treatment rates reduced liver-related deaths to 3.3/100,000, a 57% reduction from 2015. Further doubling the antibody testing rates can achieve the WHO’s mortality target in 2035, but not in 2030. Compared to the status quo, such program would be cost-effective considering a 50,000 CAD/QALY gained threshold if annual implementation costs stayed under 2.3 M CAD/100,000 people. Conclusions: Doubling the antibody testing rates, along with increased RNA testing and treatment rates, showed promise in meeting the WHO’s goals by 2035.

Background. Data on the economic burden of chronic hepatitis C (CHC) among immigrants are limited. Our objective was to estimate the CHC-attributable mortality and healthcare costs among immigrants in Ontario, Canada. Methods. We conducted a population-based matched cohort study among immigrants diagnosed with CHC between May 31, 2003, and December 31, 2018, using linked health administrative data. Immigrants with CHC (exposed) were matched 1 : 1 to immigrants without CHC (unexposed) using a combination of hard (index date, sex, and age) and propensity-score matching. Net costs (2020 Canadian dollars) collected from the healthcare payer perspective were calculated using a phase-of-care approach and used to estimate long-term costs adjusted for survival. Results. We matched 5,575 exposed individuals with unexposed controls, achieving a balanced match. The mean age was 47 years, and 52% was male. On average, 10.5% of exposed and 3.5% of unexposed individuals died 15 years postindex (relative risk = 2.9; 95% confidence interval (CI): 2.6–3.5). The net 30-day costs per person were $88 (95% CI: 55 to 122) for the prediagnosis, $324 (95% CI: 291 to 356) for the initial phase, $1,016 (95% CI: 900 to 1,132) for the late phase, and $975 (95% CI: −25 to 1,974) for the terminal phase. The mean net healthcare cost adjusted for survival at 15 years was $90,448. Conclusions. Compared to unexposed immigrants, immigrants infected with CHC have higher mortality rates and greater healthcare costs. These findings will support the planning of HCV elimination efforts among key risk groups in the province.

To achieve hepatitis C virus (HCV) elimination, high uptake along the care cascade steps for all will be necessary. We mapped engagement with the care cascade overall and among priority groups in the post-direct-acting antivirals (DAAs) period and assessed if this changed relative to pre-DAAs. We created a population-based cohort of all reported HCV diagnoses in Quebec (1990–2018) and constructed the care cascade [antibody diagnosed, RNA tested, RNA positive, genotyped, treated, sustained virologic response (SVR)] in 2013 and 2018. Characteristics associated with RNA testing and treatment initiation were investigated using marginal logistic models via generalized estimating equations. Of the 31,439 individuals HCV-diagnosed in Quebec since 1990 and alive as of 2018, there was significant progress in engagement with the care cascade post- vs. pre-DAAs; 86% vs. 77% were RNA-tested, and 64% vs. 40% initiated treatment. As of 2018, a higher risk of not being RNA-tested or treated was observed among individuals born 1965 [hazard ratio (HR); 95% CI; 1.35 (1.16–1.57)], those with material and social deprivation [1.21 (1.06–1.38)], and those with alcohol use disorder [1.21 (1.08–1.360]. Overall, non-immigrants had lower rates of RNA testing [0.76 (0.67–0.85)] and treatment initiation [0.63 (0.57–0.70)] than immigrants. As of 2018, PWID had a lower risk of not being RNA tested [0.67 (0.61–0.85)] but a similar risk of not being treated, compared to non-PWID. Engagement in the HCV care cascade have improved in the post-DAA era, but inequities remain. Vulnerable subgroups, including certain older immigrants, were less likely to have received RNA testing or treatment as of 2018 and would benefit from focused interventions to strengthen these steps.