SARS-COV-2 SEROPREVALENCE IN EMPLOYEES OF FOUR ESSENTIAL NON-HEALTHCARE SECTORS AT MODERATE/HIGH RISK OF EXPOSURE TO CORONAVIRUS INFECTION: DATA FROM THE "FIRST WAVE".

OBJECTIVE: to evaluate SARS-CoV-2 seroprevalence in Swiss non-healthcare employees at a moderate to high risk of exposure: bus drivers; supermarket, laundry service, and mail-sorting center employees. METHODS: Data on 455 essential workers included demographics, SARS-CoV-2 exposure and use of protective measures. Anti-SARS-CoV-2 IgG and IgA targeting the spike protein were measured between May and July 2020. RESULTS: The overall crude seroprevalence estimate (15.9%, 95% CI = 12.6-19.7) among essential workers was not significantly higher than that of the general working-age population (11.2%, 95% CI = 7.1-15.2). Seroprevalence ranged from 11.9% (95% CI = 6.3-19.8) among bus drivers to 22.0% (95% CI = 12.6-19.7) among food supermarket employees. CONCLUSIONS: We found no significant difference in seroprevalence between our sample of essential workers and local working-age population during the first lockdown phase of the COVID-19 pandemic. Having a seropositive housemate was the strongest predictor of SARS-CoV-2 seropositivity.

Adherence to Coronavirus Disease 2019 Preventive Measures in a Representative Sample of the Population of the Canton of Vaud, Switzerland.

Objectives: We quantified adherence to COVID-19 preventive measures and explored associated factors, after the first and during the second Swiss epidemic waves. Methods: With an observational cohort study in a representative sample of individuals aged 15 years and more, we analysed the association between self-reported adherence to COVID-19 preventive measures (respect of simple hygiene rules; respect of social distancing rules; wearing a mask) and socio-demographic factors, the existence of a chronic disease, and the existence of a previous confirmed COVID-19 episode. Results: Highest adherence was to simple hygiene rules, followed by social distancing rules and mask wearing, with a slight decrease for simple hygiene rules and a strong increase for mask wearing between visits. Men were significantly less likely to respect simple hygiene rules and wear a mask in public. Participants aged 65 years and more (versus 25-64 years) and those with at least one chronic disease (versus none) were two times more likely to respect social distancing rules and wear a mask. Conclusion: Adherence to social distancing rules and mask wearing was rather poor, especially compared to other countries.

Corona Immunitas: study protocol of a nationwide program of SARS-CoV-2 seroprevalence and seroepidemiologic studies in Switzerland.

OBJECTIVES: Seroprevalence studies to assess the spread of SARS-CoV-2 infection in the general population and subgroups are key for evaluating mitigation and vaccination policies and for understanding the spread of the disease both on the national level and for comparison with the international community. METHODS: Corona Immunitas is a research program of coordinated, population-based, seroprevalence studies implemented by Swiss School of Public Health (SSPH+). Over 28,340 participants, randomly selected and age-stratified, with some regional specificities will be included. Additional studies in vulnerable and highly exposed subpopulations are also planned. The studies will assess population immunological status during the pandemic. RESULTS: Phase one (first wave of pandemic) estimates from Geneva showed a steady increase in seroprevalence up to 10.8% (95% CI 8.2-13.9, n = 775) by May 9, 2020. Since June, Zurich, Lausanne, Basel City/Land, Ticino, and Fribourg recruited a total of 5973 participants for phase two thus far. CONCLUSIONS: Corona Immunitas will generate reliable, comparable, and high-quality serological and epidemiological data with extensive coverage of Switzerland and of several subpopulations, informing health policies and decision making in both economic and societal sectors. ISRCTN Registry: https://www.isrctn.com/ISRCTN18181860 .

Prevalence of SARS-CoV-2 in Household Members and Other Close Contacts of COVID-19 Cases: A Serologic Study in Canton of Vaud, Switzerland.

BACKGROUND: Research on severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) transmission within households and other close settings using serological testing is scarce. METHODS: We invited coronavirus disease 2019 (COVID-19) cases diagnosed between February 27 and April 1, 2020, in Canton of Vaud, Switzerland, to participate, along with household members and other close contacts. Anti-SARS-CoV-2 immunoglobulin G antibodies were measured using a Luminex immunoassay. We estimated factors associated with serological status using generalized estimating equations. RESULTS: Overall, 219 cases, 302 household members, and 69 other close contacts participated between May 4 and June 27, 2020. More than half of household members (57.2%; 95% CI, 49.7%-64.3%) had developed a serologic response to SARS-CoV-2, while 19.0% (95% CI, 10.0%-33.2%) of other close contacts were seropositive. After adjusting for individual and household characteristics, infection risk was higher in household members aged ≥65 years than in younger adults (adjusted odds ratio [aOR], 3.63; 95% CI, 1.05-12.60) and in those not strictly adhering to simple hygiene rules like hand washing (aOR, 1.80; 95% CI, 1.02-3.17). The risk was lower when more than 5 people outside home were met during semiconfinement, compared with none (aOR, 0.35; 95% CI, 0.16-0.74). Individual risk of household members to be seropositive was lower in large households (22% less per each additional person). CONCLUSIONS: During semiconfinement, household members of a COVID-19 case were at very high risk of getting infected, 3 times more than close contacts outside home. This highlights the need to provide clear messages on protective measures applicable at home. For elderly couples, who were especially at risk, providing external support for daily basic activities is essential.