Seroprevalence of IgG antibodies against SARS coronavirus 2 in Belgium – a serial prospective cross-sectional nationwide study of residual samples (March – October 2020)

Abstract

Background In the first weeks of the COVID-19 epidemic in Belgium, a repetitive national serum collection was set up to monitor age-related exposure through emerging SARS-CoV-2 antibodies. First objective was to estimate the baseline seroprevalence and seroincidence using serial survey data that covered the start of a national lock-down period installed soon after the epidemic was recognized. Methods A prospective serial cross-sectional seroprevalence study, stratified by age, sex and region, started with two collections in April 2020. In residual sera taken outside hospitals and collected by diagnostic laboratories, IgG antibodies against S1 proteins of SARS-CoV-2 were measured with a semi-quantitative commercial ELISA. Seropositivity (cumulative, by age category and sex) and seroincidence over a 3 weeks period were estimated for the Belgian population. Findings In the first collection, IgG antibodies were detected in 100 out of 3910 samples, whereas in the second collection 193 out of 3391 samples were IgG positive. The weighted overall seroprevalence increased from 2.9% (95% CI 2.3 to 3.6) to 6.0% (95% CI 5.1 to 7.1), reflected in a seroincidence estimate of 3.1% (95% CI 1.9 to 4.3). Age-specific seroprevalence significantly increased in the age categories 20-30, 80-90 and ≥90. No significant sex effect was observed. Interpretation During the start of epidemic mitigation by lockdown, a small but increasing fraction of the Belgian population showed serologically detectable signs of exposure to SARS-CoV-2. Funding This independent researcher-initiated study acknowledges financial support from the Antwerp University Fund, the Flemish Research Fund, and European Horizon 2020.

SARS-CoV-2 Infections and Impact of the COVID-19 Pandemic in Pregnancy and Breastfeeding: Results from an Observational Study in Primary Care in Belgium

“…At that time, 0.3% of the more than 6400 pregnant and breastfeeding women reported to have tested positive for SARS-CoV-2. This percentage is substantially lower than the seroprevalence of 3-6% measured in the general population in Belgium in April 2020 [16]. Importantly, the estimates observed in our sample are undoubtedly underestimations of the actual prevalence due to the potential of an asymptomatic course of COVID-19 in pregnancy and to the lack of systematic testing in Belgium at the time of the survey completion [17,18].…”

“…Importantly, the estimates observed in our sample are undoubtedly underestimations of the actual prevalence due to the potential of an asymptomatic course of COVID-19 in pregnancy and to the lack of systematic testing in Belgium at the time of the survey completion [17,18]. However, even in the most extreme scenario when up to 85% of the infected pregnant respondents were asymptomatic [17,18], and were thus not tested and diagnosed, the seroprevalence of COVID-19 in our sample would not exceed the percentage observed in the general population [16]. In addition, the test positivity rate in our pregnant sample, despite the limited number of cases, is not higher than the rate obtained in the general population in the same period (i.e., 15-25%) [19].…”

Seroprevalence of SARS-CoV-2 among adults in three regions of France following the lockdown and associated risk factors: a multicohort study

“…26 They were also in the range reported in similar studies in Europe. 4,5,[7][8][9] Half of the participants with a positive ELISA-S had an episode corresponding to the definition of a COVID-19 case, and the reported symptoms corresponded to those described in similar studies. 5,7 One in five positive participants did not experience any symptoms from the onset of the pandemic.…”

Serological identification of SARS-CoV-2 infections among children visiting a hospital during the initial Seattle outbreak

“…However, as noted above, the frequency of seropositive samples in our study population is roughly similar to estimates of cumulative all-age incidence in Seattle based on testing and mortality data 20,21 . Comparing across age groups remains an important area for further investigation, as other very recent serosurveys that included both children and adults have reached differing conclusions about whether prevalence differs 39,40 . In any case, our work shows how serological assays can identify pediatric infections missed by the symptom-based administration of viral tests, as most seropositive children in our study had never tested positive for the virus.…”