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ObjectivesThis cohort study including essential workers, assessed the□risk and incidence of SARS-CoV-2□infection during the second surge of COVID-19 according to baseline serostatus and occupational sector.MethodsEssential workers were selected from a seroprevalence survey cohort in Geneva, Switzerland and were linked to a state centralized registry compiling SARS-CoV-2 infections. Primary outcome was the number of virologically-confirmed infections from serological assessment (between May and September 2020) to January 25, 2021, according to baseline antibody status and stratified by three pre-defined occupational groups (occupations requiring sustained physical proximity, involving brief regular contact or others). Secondary outcomes included the incidence of infection.Results10457 essential workers were included (occupations requiring sustained physical proximity accounted for 3057 individuals, those involving regular brief contact, 3645, and 3755 workers were classified under “Other essential occupations”). After a follow-up period of over 27 weeks, 5 (0.6%) seropositive and 830 (8.5%) seronegative individuals had a positive SARS-CoV-2 test, with an incidence rate of 0.2 (95% CI 0.1 to 0.6) and 3.2 (95% CI 2.9 to 3.4) cases per person-week, respectively. Incidences were similar across occupational groups. Seropositive essential workers had a 93% reduction in the hazard (HR of 0.07, 95% CI 0.03 to 0.17) of having a positive test during follow-up with no significant between-occupational group difference.ConclusionsA ten-fold reduction in the hazard of being virologically tested positive was observed among anti-SARS-CoV-2 seropositive essential workers regardless of their sector of occupation, confirming the seroprotective effect of a previous SARS-CoV2 exposure at least six months after infection.Key messagesWhat is already known about this subject?Risk of SARS-CoV-2 reinfection is low in the general population and among healthcare workers.What are the new findings?A ten-fold reduction of risk of being virologically tested positive reinfection is observed among anti-SARS-CoV-2 seropositive essential workers of different activity sectors, regardless of their occupation-related risk of exposure.How might this impact on policy or clinical practice in the foreseeable future?Vaccination could be delayed in individuals with previous history of SARS-CoV-2 infection with serologic confirmation, regardless of their occupational exposure. These observations need to be confirmed for new SARS-CoV-2 variants.

We report a prospective epidemiological, virological and serological investigation of a SARS-CoV-2 outbreak in a primary school, as part of a longitudinal, prospective, primary school-based surveillance study. It involved repeated testing of pupils and teachers and household members of participants who tested positive, with rapid antigen tests and/or RT-PCR (Day 0-2 and Day 5-7), serologies on dried capillary blood samples (Day 0-2 and Day 30), contact tracing interviews and SARS-CoV-2 whole genome sequencing. This SARS-CoV-2 outbreak caused by the Alpha variant involved 20 children aged 4 to 6 years from 4 classes, 2 teachers and a total of 4 household members. Infection attack rates were between 11.8 and 62.0% among pupils from the 4 classes, 22.2% among teachers and 0% among non-teaching staff. Secondary attack rate among household members was 15.4%. Symptoms were reported by 63% of infected children, 100% of teachers and 50% of household members. All analysed sequences but one showed 100% identity. Serological tests detected 8 seroconversions unidentified by SARS-CoV-2 virological tests. This study confirmed child-to-child and child-to-adult transmission of the infection. Effective measures to limit transmission in schools have the potential to reduce the overall community circulation.

BackgroundUp-to-date seroprevalence estimates are critical to describe the SARS-CoV-2 immune landscape in the population and guide public health measures. We aimed to estimate the seroprevalence of anti-SARS-CoV-2 antibodies 15 months into the COVID-19 pandemic and six months into the vaccination campaign.MethodsWe conducted a population-based cross-sectional serosurvey between June 1 and July 7, 2021, recruiting participants from age- and sex-stratified random samples of the general population. We tested participants for anti-SARS-CoV-2 antibodies targeting the spike (S) or nucleocapsid (N) proteins (Roche Elecsys immunoassays). We estimated the anti-SARS-CoV-2 antibodies seroprevalence following vaccination and/or infection (anti-S antibodies), or infection only (anti-N antibodies).ResultsWe included 3355 individuals, of which 1814 (54.1%) were women, 697 (20.8%) were aged ConclusionsMost adults have developed anti-SARS-CoV-2 antibodies, while most teenagers and children remain vulnerable to infection. As the SARS-CoV-2 Delta variant spreads and vaccination rates stagnate, efforts are needed to address vaccine hesitancy, particularly among younger individuals and socioeconomically disadvantaged groups, and to minimize spread among children.

ObjectiveThis study aimed to assess acceptance of COVID-19 vaccination as well as its sociodemographic and clinical determinants in a general population sample three months after the launch of the vaccination program in Switzerland.MethodsIn March 2021, an online questionnaire on vaccination acceptance was proposed to adults included in a longitudinal cohort study of previous population-based serosurveys carried out in the canton of Geneva. Questions were asked about COVID-19 vaccination acceptance, reasons of acceptance or refusal, and attitudes about vaccination in general. Data on demographic (age, sex, education, income, professional status, living conditions) and health-related characteristics (having a chronic disease, COVID-19 diagnosis, smoking status) were assessed at inclusion in the cohort (December 2020).ResultsOverall, 4’067 participants (completion rate of 77.4%) responded to the survey between March 17 and April 1, 2021. The mean age of respondents was 53.3 years and 56.0% were women. Most had completed tertiary education (64.7%) and over 60% were currently professionally active. At the time of the survey, 17.2% of respondents had already been vaccinated with at least one dose or had made an appointment to get vaccinated, and an additional 58.5% intended or rather intended to get vaccinated. The overall acceptance of COVID-19 vaccination was 75.7%, with a higher acceptance among men compared to women, older adults compared to younger adults, high-income individuals compared to those with a low income, participants living in urban and semi-urban areas compared to rural, and retirees and students compared to employed individuals. Acceptance was lower among individuals having completed apprenticeships and secondary education compared to those with tertiary education. The most common reasons reported by participants intending to get vaccinated were the desire to ‘get back to normal’, to protect themselves, their community and/or society, and their relatives or friends against the risk of infection by SARS-CoV-2, as well as the desire to travel. Less than half (45.6%) of participants having children were willing or rather willing to have their children vaccinated against COVID-19 if it were recommended by public health authorities.ConclusionAlthough our study found a 75.7% acceptance of COVID-19 vaccination, there were noticeable socio-demographic disparities in vaccination acceptance. These data will be useful for public health measures targeting hesitant populations when developing health communication strategies. These results will be updated over time with a new release of the survey in autumn 2021.

Limited data exist on SARS-CoV-2 infection rates across sectors and occupations, hindering our ability to make rational policy, including vaccination prioritization, to protect workers and limit SARS-CoV-2 spread. Here, we present results from our SEROCoV-WORK + study, a serosurvey of workers recruited after the first wave of the COVID-19 pandemic in Geneva, Switzerland. We tested workers (May 18—September 18, 2020) from 16 sectors and 32 occupations for anti-SARS-CoV-2 IgG antibodies. Of 10,513 participants, 1026 (9.8%) tested positive. The seropositivity rate ranged from 4.2% in the media sector to 14.3% in the nursing home sector. We found considerable within-sector variability: nursing home (0%–31.4%), homecare (3.9%–12.6%), healthcare (0%–23.5%), public administration (2.6%–24.6%), and public security (0%–16.7%). Seropositivity rates also varied across occupations, from 15.0% among kitchen staff and 14.4% among nurses, to 5.4% among domestic care workers and 2.8% among journalists. Our findings show that seropositivity rates varied widely across sectors, between facilities within sectors, and across occupations, reflecting a higher exposure in certain sectors and occupations., Many job sectors classified as ‘essential’ have continued operating with limited restrictions during the COVID-19 pandemic, potentially placing workers at higher risk of infection. Here, the authors show that seropositivity rates in workers vary widely across and between job sectors in Geneva, Switzerland.

ImportanceSerological assays detecting specific IgG antibodies generated against the Spike protein following Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) infection are being widely deployed in research studies and clinical practice. However, the duration and the effectiveness of the protection conferred by the immune response against future infection remains to be assessed in a large population.ObjectiveTo estimate the incidence of newly acquired SARS-CoV-2 infections in seropositive individuals from a population-based sample as compared to seronegative controls.DesignRetrospective longitudinal propensity-score matched cohort study.SettingA seroprevalence survey including a population-based representative sample of the population from the canton of Geneva (Switzerland) was conducted between April and June 2020, immediately after the first pandemic wave. Each individual included in the seroprevalence survey was linked to a state centralized registry compiling virologically confirmed SARS-CoV-2 infections since the beginning of the pandemic.ParticipantsParticipants aged twelve years old and over, who developed anti-spike IgG antibodies were matched one-to-two to seronegative controls, using a propensity-score including age, gender, immunodeficiency, body mass index, smoking status and education level.ExposureSARS-CoV-2 seropositivity.Main outcomes and measuresOur primary outcome was virologically confirmed SARS-CoV-2 infections which occurred from serological status assessment in April-June 2020 to the end of the second pandemic wave (January 2021). Additionally, incidence of infections, rate of testing and proportion of positive tests were analysed.ResultsAmong 8344 serosurvey participants, 498 seropositive individuals were selected and matched with 996 seronegative controls. After a mean follow-up of 35.6 (Standard Deviation, SD: 3.2) weeks, 7 out of 498 (1.4%) seropositive subjects had a positive SARS-CoV-2 test, of which 5 (1.0%) were considered as reinfections. By contrast, infection rate was significantly higher in seronegative individuals (15.5%, 154/996) during a similar mean follow-up of 34.7 (SD 3.2) weeks, corresponding to a 94% (95%CI 86% to 98%,PConclusions and relevanceSeroconversion after SARS-CoV-2 infection confers protection to successive viral contamination lasting at least 8 months. These findings could help global health authorities establishing priority for vaccine allocation.Key pointsQuestionDo SARS-CoV-2 antibodies confer protection against future infection?FindingsIn this retrospective matched cohort study nested in a representative sample of the general population of Geneva, Switzerland, we observed a 94% reduction in the hazard of being infected among participants with antibodies against SARS-CoV-2, when compared to seronegative controls, >8 months after initial serology assessment.MeaningSeroconversion to SARS-CoV-2 is associated with a large and sustained protection against reinfection.

Serologic studies have been critical in tracking the evolution of the COVID-19 pandemic. The reliability of serologic studies for quantifying the proportion of the population that have been infected depends on the extent of antibody decay as well as on assay performance in detecting both recent and older infections. Data on anti-SARS-CoV-2 antibodies persistence remain sparse, especially from infected individuals with few to no symptoms. In a cohort of mostly mild/asymptomatic SARS-CoV-2-infected individuals tested with three widely-used immunoassays, antibodies persisted for at least 8 months after infection, although detection depended on immunoassay choice, with one of them missing up to 40% of past infections. Simulations reveal that without appropriate adjustment for time-varying assay sensitivity, seroprevalence surveys may underestimate infection rates. As the immune landscape becomes more complex with naturally-infected and vaccinated individuals, assay choice and appropriate assay-performance-adjustment will become even more important for the interpretation of serologic studies.

Background Serological assays detecting anti-severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antibodies are being widely deployed in studies and clinical practice. However, the duration and effectiveness of the protection conferred by the immune response remains to be assessed in population-based samples. To estimate the incidence of newly acquired SARS-CoV-2 infections in seropositive individuals as compared to seronegative controls, we conducted a retrospective longitudinal matched study. Methods A seroprevalence survey including a representative sample of the population was conducted in Geneva, Switzerland, between April and June 2020, immediately after the first pandemic wave. Seropositive participants were matched one-to-two to seronegative controls, using a propensity-score including age, gender, immunodeficiency, body mass index (BMI), smoking status, and education level. Each individual was linked to a state-registry of SARS-CoV-2 infections. Our primary outcome was confirmed infections occurring from serological status assessment to the end of the second pandemic wave (January 2021). Results Among 8344 serosurvey participants, 498 seropositive individuals were selected and matched with 996 seronegative controls. After a mean follow-up of 35.6 (standard deviation [SD] 3.2) weeks, 7 out of 498 (1.4%) seropositive subjects had a positive SARS-CoV-2 test, of whom 5 (1.0%) were classified as reinfections. In contrast, the infection rate was higher in seronegative individuals (15.5%, 154/996) during a similar follow-up period (mean 34.7 [SD 3.2] weeks), corresponding to a 94% (95% confidence interval [CI]: 86%– 98%, P Conclusions Seroconversion after SARS-CoV-2 infection confers protection against reinfection lasting at least 8 months. These findings could help global health authorities establishing priority for vaccine allocation.

Background Up-to-date seroprevalence estimates are critical to describe the SARS-CoV-2 immune landscape and to guide public health decisions. Aim We estimate seroprevalence of anti-SARS-CoV-2 antibodies 15 months into the COVID-19 pandemic and 6 months into the vaccination campaign. Methods We conducted a population-based cross-sectional serosurvey between 1 June and 7 July 2021, recruiting participants from age- and sex-stratified random samples of the general population. We tested participants for anti-SARS-CoV-2 antibodies targeting the spike (S) or nucleocapsid (N) proteins using the Roche Elecsys immunoassays. We estimated the anti-SARS-CoV-2 antibodies seroprevalence following vaccination and/or infection (anti-S antibodies), or infection only (anti-N antibodies). Results Among 3,355 individuals (54.1% women; 20.8% aged Conclusion Most of the population has developed anti-SARS-CoV-2 antibodies, despite most teenagers and children remaining vulnerable to infection. As the SARS-CoV-2 Delta variant spreads and vaccination rates stagnate, efforts are needed to address vaccine hesitancy, particularly among younger individuals and to minimise spread among children.

OBJECTIVE: This study aimed to assess the public perception of COVID-19 vaccination certificates as well as potential differences between individuals. METHODS: Between 17 March and 1 April 2021, a self-administered online questionnaire was proposed to all persons aged 18 years and older participating in the longitudinal follow-up of SARS-CoV-2 seroprevalence studies in Geneva, Switzerland. The questionnaire covered aspects of individual and collective benefits, and allowed participants to select contexts in which vaccination certificates should be presented. Results were presented as the proportion of persons agreeing or disagreeing with the implementation of vaccination certificates, selecting specific contexts where certificates should be presented, and agreeing or disagreeing with the potential risks related to certificates. Logistic regression was used to calculate odds ratios for factors associated with certificate non-acceptance. RESULTS: Overall, 4067 individuals completed the questionnaire (response rate 77.4%; mean age 53.3 ± standard deviation 14.4 years; 56.1% were women). About 61.0% of participants agreed or strongly agreed that a vaccination certificate was necessary in certain contexts and 21.6% believed there was no context where vaccination certificates should be presented. Contexts where a majority of participants perceived a vaccination certificate should be presented included jobs where others would be at risk of COVID-related complications (60.7%), jobs where employees would be at risk of getting infected (58.7%), or to be exempt from quarantine when travelling abroad (56.0%). Contexts where fewer individuals perceived the need for vaccination certificates to be presented were participation in large gatherings (36.9%), access to social venues (35.5%), or sharing the same workspace (21.5%). Younger age, no intent for vaccination, and not believing vaccination to be an important step in surmounting the pandemic were factors associated with certificate non-acceptance. CONCLUSION: This large population-based study showed that the general adult population in Geneva, Switzerland, agreed with the implementation of vaccination certificates in work-related and travel-related contexts. However, this solution was perceived as unnecessary for access to large gatherings or social venues, or to share the same workspace. Differences were seen with age, sex, education, socioeconomic status, and vaccination willingness and perception, highlighting the importance of taking personal and sociodemographic variation into consideration when predicting acceptance of such certificates.

Objectives Serological studies have been critical in tracking the evolution of the COVID-19 pandemic. Data on anti-SARS-CoV-2 antibodies persistence remain sparse, especially from infected individuals with few to no symptoms. The objective of the study was to quantify the sensitivity for detecting historic SARS-CoV-2 infections as a function of time since infection for three commercially available SARS-CoV-2 immunoassays and to explore the implications of decaying immunoassay sensitivity in estimating seroprevalence. Methods We followed a cohort of mostly mild/asymptomatic SARS-CoV-2-infected individuals (n = 354) at least 8 months after their presumed infection date and tested their serum for anti-SARS-CoV-2 antibodies with three commercially available assays: Roche-N, Roche-RBD and EuroImmun-S1. We developed a latent class statistical model to infer the specificity and time-varying sensitivity of each assay and show through simulations how inappropriately accounting for test performance can lead to biased serosurvey estimates. Results Antibodies were detected at follow-up in 74–100% of participants, depending on immunoassays. Both Roche assays maintain high sensitivity, with the EuroImmun assay missing 40% of infections after 9 months. Simulations reveal that without appropriate adjustment for time-varying assay sensitivity, seroprevalence surveys may underestimate infection rates. Discussion Antibodies persist for at least 8 months after infection in a cohort of mildly infected individuals with detection depending on assay choice. Appropriate assay performance adjustment is important for the interpretation of serological studies in the case of diminishing sensitivity after infection.