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

  1. Silvia Stringhini
  2. María-Eugenia Zaballa
  3. Nick Pullen
  4. Javier Perez-Saez
  5. Carlos de Mestral
  6. Andrea Jutta Loizeau
  7. Julien Lamour
  8. Francesco Pennacchio
  9. Ania Wisniak
  10. Roxane Dumont
  11. Hélène Baysson
  12. Viviane Richard
  13. Elsa Lorthe
  14. Claire Semaani
  15. Jean-François Balavoine
  16. Didier Pittet
  17. Nicolas Vuilleumier
  18. François Chappuis
  19. Omar Kherad
  20. Andrew S. Azman
  21. Klara Posfay-Barbe
  22. Laurent Kaiser
  23. Idris Guessous
  24. on behalf of the Specchio-COVID19 study group

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Abstract

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 < 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.

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.

Article activity feed

  1. Version published to 10.2807/1560-7917.es.2021.26.43.2100830
  2. ScreenIT

    SciScore for 10.1101/2021.08.12.21261929: (What is this?)

    Please note, not all rigor criteria are appropriate for all manuscripts.

    Table 1: Rigor

    EthicsIRB: 6,8 The Geneva Cantonal Commission for Research Ethics approved this study (Project N° 2020-00881).
    Consent: Participants gave written consent, provided a venous blood sample, and completed a questionnaire.
    Sex as a biological variablenot detected.
    RandomizationStudy design and participants: We conducted a cross-sectional serosurvey between June 1 and July 7, 2021, recruiting participants from a random sample of individuals aged 0-64 years provided by the Swiss Federal Office of Statistics, and an age- and sex-stratified random sample of individuals aged 18-24 years and ≥50 years from a previous serosurvey using the same methodology (Addendum S1 in Supplementary Material).
    Blindingnot detected.
    Power Analysisnot detected.

    Table 2: Resources

    Antibodies
    SentencesResources
    Since the vaccines used to date in Geneva elicit no response to the SARS-CoV-2 N-protein, we used participants’ two-marker antibody profiles to estimate the proportion having any anti-SARS-CoV-2 antibody and the proportion having antibodies due to infection (but could also have been vaccinated).
    anti-SARS-CoV-2
    suggested: None

    Results from OddPub: We did not detect open data. We also did not detect open code. Researchers are encouraged to share open data when possible (see Nature blog).

    Results from LimitationRecognizer: We detected the following sentences addressing limitations in the study:
    Limitations include the fact that, as with most seroprevalence surveys,27 the sample was generally more socioeconomically advantaged than the general population (Table S4), which may have led to overestimation of vaccine-derived antibody seroprevalence—however, the proportion of vaccinated individuals in our sample was similar to that observed in the general population of Geneva (Table S5); the fact that we only included formal residents and that we only assessed education as a socioeconomic indicator, which may have precluded the identification of inequalities based on other indicators; and, finally, the fact that, since we did not perform neutralization assays, our estimates may not completely reflect SARS-CoV-2 protective immunity.28 This study provides the first seroprevalence estimates of SARS-CoV-2 antibodies in a representative sample of the general population after the third pandemic wave and the start of mass vaccination. Our findings highlight how mass vaccination has closed the immunity gap in most of the adult population—particularly among older individuals who are at the greatest risk of severe COVID-19 outcomes.29 They attest to the efficacy of free-of-charge vaccination programs in promoting immunization against the virus while highlighting the need to strengthen efforts to address vaccine hesitancy.21,23 Importantly, our findings also show that the large majority of children and teenagers, and a large proportion of young and middle-aged adults, lack anti-SARS-...

    Results from TrialIdentifier: No clinical trial numbers were referenced.

    Results from Barzooka: We did not find any issues relating to the usage of bar graphs.

    Results from JetFighter: We did not find any issues relating to colormaps.

    Results from rtransparent:
    • Thank you for including a conflict of interest statement. Authors are encouraged to include this statement when submitting to a journal.
    • Thank you for including a funding statement. Authors are encouraged to include this statement when submitting to a journal.
    • No protocol registration statement was detected.

    Results from scite Reference Check: We found no unreliable references.

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  3. Version published to 10.1101/2021.08.12.21261929 on medRxiv