SARS-CoV-2 Seroprevalence in Germany

Abstract

Background: Until now, information on the spread of SARS-CoV-2 infections in Germany has been based mainly on data from the public health offices. It may be assumed that these data do not include many cases of asymptomatic and mild infection.

Methods: We determined seroprevalence over the course of the pandemic in a sequential, multilocal seroprevalence study (MuSPAD). Study participants were recruited at random in seven administrative districts (Kreise) in Germany from July 2020 onward; each participant was tested at two different times 3-5 months apart. Test findings on blood samples were used to determine the missed-case rate of reported infections, the infection fatality rate (IFR), and the association between seropositivity and demographic, socio-economic, and health-related factors, as well as to evaluate the self-reported results of PCR and antigenic tests. The registration number of this study is DRKS00022335.

Results: Among non-vaccinated persons, the seroprevalence from July to December 2020 was 1.3-2.8% and rose between February and May 2021 to 4.1-13.1%. In July 2021, 35% of tested persons in Chemnitz were not vaccinated, and the seroprevalence among these persons was 32.4% (07/2021). The surveillance detection ratio (SDR), i.e., the ratio between the true number of infections estimated from seroprevalence and the actual number or reported infections, varied among the districts included in the study from 2.2 to 5.1 up to December 2020 and from 1.3 to 2.9 up to June 2021, and subsequently declined. The IFR was in the range of 0.8% to 2.4% in all regions except Magdeburg, where a value of 0.3% was calculated for November 2020. A lower educational level was associated with a higher seropositivity rate, smoking with a lower seropositivity rate. On average, 1 person was infected for every 8.5 persons in quarantine.

Conclusion: Seroprevalence was low after the first wave of the pandemic but rose markedly during the second and third waves. The missed-case rate trended downward over the course of the pandemic.

Figure

Timeline of weighted SARS-CoV-2 seropositivity (SP), infection fatality rate (IFR), and the Surveillance Detection Ratio (SDR) with 95% confidence intervals based on ELISA (Euroimmun) results, together with the vaccine coverage for the first and second doses (Vacc. 1, Vacc.2) for seven MuSPAD study sites, Germany, July 2020 to August 2021

eFigure

Weighted seroprevalence in unvaccinated study participants. Vaccinated and follow-up participants were excluded from analysis. The weighting depended on the age- and sex-specific distribution of the total population of the respective study location. The numbers of reported COVID-19 deaths at the beginning of the study are based on data from the collaboration portal COVID-19 Data Hub of the Robert Koch Institute 2021. *¹ Follow-up participants; *² logistics-related data loss; *³ positive vaccination status