Seroprevalence of IgG antibodies against SARS-CoV-2 – a serial prospective cross-sectional nationwide study of residual samples, Belgium, March to October 2020

  1. Sereina Annik Herzog
  2. Jessie De Bie
  3. Steven Abrams
  4. Ine Wouters
  5. Esra Ekinci
  6. Lisbeth Patteet
  7. Astrid Coppens
  8. Sandy De Spiegeleer
  9. Philippe Beutels
  10. Pierre Van Damme
  11. Niel Hens
  12. Heidi Theeten

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Abstract

To control epidemic waves, it is important to know the susceptibility to SARS-CoV-2 and its evolution over time in relation to the control measures taken.

Aim

To assess the evolving SARS-CoV-2 seroprevalence and seroincidence related to the first national lockdown in Belgium, we performed a nationwide seroprevalence study, stratified by age, sex and region using 3,000–4,000 residual samples during seven periods between 30 March and 17 October 2020.

Methods

We analysed residual sera from ambulatory patients for IgG antibodies against the SARS-CoV-2 S1 protein with a semiquantitative commercial ELISA. Weighted seroprevalence (overall and by age category and sex) and seroincidence during seven consecutive periods were estimated for the Belgian population while accommodating test-specific sensitivity and specificity.

Results

The weighted overall seroprevalence initially increased from 1.8% (95% credible interval (CrI): 1.0–2.6) to 5.3% (95% CrI: 4.2–6.4), implying a seroincidence of 3.4% (95% CrI: 2.4–4.6) between the first and second collection period over a period of 3 weeks during lockdown (start lockdown mid-March 2020). Thereafter, seroprevalence stabilised, however, significant decreases were observed when comparing the third with the fifth, sixth and seventh period, resulting in negative seroincidence estimates after lockdown was lifted. We estimated for the last collection period mid-October 2020 a weighted overall seroprevalence of 4.2% (95% CrI: 3.1–5.2).

Conclusion

During lockdown, an initially small but increasing fraction of the Belgian population showed serologically detectable signs of exposure to SARS-CoV-2, which did not further increase when confinement measures eased and full lockdown was lifted.

Article activity feed

  1. Version published to 10.2807/1560-7917.es.2022.27.9.2100419
  2. Version published to 10.1101/2020.06.08.20125179v6 on medRxiv
  3. Version published to 10.1101/2020.06.08.20125179v5 on medRxiv
  4. Version published to 10.1101/2020.06.08.20125179v4 on medRxiv
  5. Version published to 10.1101/2020.06.08.20125179v3 on medRxiv
  6. Version published to 10.1101/2020.06.08.20125179v2 on medRxiv
  7. ScreenIT

    SciScore for 10.1101/2020.06.08.20125179: (What is this?)

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

    Table 1: Rigor

    NIH rigor criteria are not applicable to paper type.

    Table 2: Resources

    Antibodies
    SentencesResources
    9 Presence of detectable IgG antibodies indicates prior exposure to SARS-CoV-2, an infection which may be resolved or is still resolving, and possibly protection against reinfection.8,10 Data management: Data collected for each sample include: unique sample code, sample date, age, sex, and postal code of the place of residence.
    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: An explicit section about the limitations of the techniques employed in this study was not found. We encourage authors to address study limitations.

    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.

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  8. Version published to 10.1101/2020.06.08.20125179v1 on medRxiv