Nationwide population-based infection- and vaccine-induced SARS-CoV-2 seroprevalence in Germany at the end of 2021

Summary Background The first wave of the Corona Monitoring Nationwide (RKI-SOEP) Study drawn from the German Socio-Economic Panel proved a low pre-vaccine SARS-CoV-2 seroprevalence in the German adult population of 2.1%. Methods In this second wave of the study (RKI-SOEP-2, November 2021-March 2022), we used combined serological and self-reported data on infection and vaccination to estimate the prevalence of SARS-CoV-2-specific anti-spike and/or anti-nucleocapsid IgG antibodies (combined seroprevalence), past infection, and basic immunization in individuals aged 14+. Findings Combined seroprevalence was 90.7% (95% CI 89.7% - 91.6%) without correction for antibody waning and 94.6% (95% CI 93.6% - 95.7%) with correction. While 1 in 10 individuals had been infected (9.9%, 95% CI 9.0% - 10.9%), 9 in 10 had at least a basic immunization (90%, 95% CI 88.9%-90.9%). Population-weighted estimates differed by age, region, and socioeconomic deprivation. Infection-induced seroprevalence with correction for antibody waning was 1.55 (95% CI 1.3 - 1.8) times higher than the cumulative proportion based on national surveillance data. Interpretation At the beginning of the SARS-CoV-2-Omicron wave, the vast majority of the population had been vaccinated, infected, or both. Our results show how large-scale vaccination, but not a high infection rate, was able to fill the immunity gap, especially in older individuals (aged 65+) who are known to be at higher risk of severe COVID-19. Our data point towards a targeted demographically and regionally stratified mitigation strategy, to optimize future pandemic mitigation efforts.