Seroprevalence of anti-SARS-CoV-2 antibodies six months after the start of the vaccination campaign in Geneva, Switzerland

Stringhini S, Zaballa ME, Pullen N, Perez-Saez J, de Mestral C, Loizeau A, Lamour J, Pennacchio F, Wisniak A, Dumont R, Baysson H, Richard V, Lorthe E, Semaani C, Balavoine JF, Pittet D, Vuilleumier N, Chappuis F, Kherad O, Azman AS., Posfay-Barbe K, Kaiser L, Guessous I, on behalf of the Specchio-COVID19 study group.
Seroprevalence of anti-SARS-CoV-2 antibodies 6 months into the vaccination campaign in Geneva, Switzerland, 1 June to 7 July 2021Euro Surveillance. 2021;26(43): doi.org/10.2807/1560-7917.ES.2021.26.43.2100830

Summary:

Background: Seroprevalence estimates are essential to describe the immune landscape of SARS-CoV-2 and guide public health decisions.

Objectives: To estimate the seroprevalence of anti-SARS-CoV-2 antibodies fifteen months after the start of the COVID-19 pandemic and six months after the start of the vaccination campaign.

Methods: We conducted a population-based cross-sectional study between 1 June and 7 July 2021. Participants were randomly recruited from general population samples stratified by age and sex. Participants were tested for anti-SARS-CoV-2 antibodies by targeting Spike (S) or Nucleocapsid (N) protein using Roche Elecsys Immunoassay. We estimated seroprevalence following vaccination and/or infection (anti-S antibodies), or infection only (anti-N antibodies).

Results: Among 3,355 individuals tested (54.1% women; 20.8% < 18 years and 13.4% aged ≥ 65 years), 2,161 (64.4%) had anti-S antibodies and 906 (27.0%) had anti-N antibodies. Total seroprevalence was 66.1% (95% credibility interval (Crl: 64.1-68.0). We estimated that 29.9% (95% Crl: 28.0-31.9) of the population developed antibodies after infection; the remainder of the population developed antibodies through vaccination. Seroprevalence estimates differed markedly by age group, being lowest in children aged 0-5 years (20.8%; 95% Crl: 15.5-26.7) and highest in people aged ≥ 75 years (93.1%; 95% Crl: 89.6-96.0). The seroprevalence of antibodies developed by infection and/or vaccination was higher among participants with a higher level of education.

Conclusion: Most of the population has developed anti-SARS-CoV-2 antibodies, but most adolescents and children remain vulnerable to infection. As the Delta variant spreads and vaccination and vaccination rates stagnate, efforts are needed to combat vaccine hesitancy, particularly among young people, and minimise spread among children.

Link to the article in English