Seroprevalence of anti-SARS-CoV-2 antibodies 6 months into the vaccination campaign in Geneva, Switzerland, 1 June to 7 July 2021

Euro Surveill. 2021 Oct;26(43):2100830. doi: 10.2807/1560-7917.ES.2021.26.43.2100830.


BackgroundUp-to-date seroprevalence estimates are critical to describe the SARS-CoV-2 immune landscape and to guide public health decisions.AimWe estimate seroprevalence of anti-SARS-CoV-2 antibodies 15 months into the COVID-19 pandemic and 6 months into the vaccination campaign.MethodsWe 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).ResultsAmong 3,355 individuals (54.1% women; 20.8% aged < 18 years and 13.4% aged ≥ 65 years), 2,161 (64.4%) had anti-S antibodies and 906 (27.0%) had anti-N antibodies. The total seroprevalence was 66.1% (95% credible interval (CrI): 64.1-68.0). We estimated that 29.9% (95% Crl: 28.0-31.9) of the population developed antibodies after infection; the rest having developed antibodies via vaccination. Seroprevalence estimates differed markedly across age groups, being lowest among children aged 0-5 years (20.8%; 95% Crl: 15.5-26.7) and highest among older adults aged ≥ 75 years (93.1%; 95% Crl: 89.6-96.0). Seroprevalence of antibodies developed via infection and/or vaccination was higher among participants with higher educational level.ConclusionMost 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.

Keywords: Anti-SARS-CoV-2 antibodies; Switzerland; population-based; seroprevalence.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adolescent
  • Aged
  • Antibodies, Viral
  • COVID-19*
  • Child
  • Child, Preschool
  • Cross-Sectional Studies
  • Female
  • Humans
  • Immunization Programs
  • Infant
  • Infant, Newborn
  • Male
  • Pandemics
  • SARS-CoV-2*
  • Seroepidemiologic Studies
  • Switzerland


  • Antibodies, Viral