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

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. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement The RKI-SOEP-2 study was funded by the German Federal Ministry of Health (project number ZMI1-2521COR305) and by using existing resources of the participating institutions. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: The study was approved by the ethics committee of the Berlin Medical Association (Eth-33/20). I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes The data cannot be made publicly available because informed consent from participants did not cover public deposition of data. However, the dataset underlying the analysis in this article is archived in the SOEP Research Data Centre (https://www.diw.de/en/diw\_01.c.601584.en/data\_access.html) in Berlin and can be accessed on site upon reasonable request. [https://www.diw.de/en/diw\_01.c.601584.en/data\_access.html][1] The data cannot be made publicly available because informed consent from participants did not cover public deposition of data. However, the dataset underlying the analysis in this article is archived in the SOEP Research Data Centre ([https://www.diw.de/en/diw\_01.c.601584.en/data\_access.html][1]) in Berlin and can be accessed on site upon reasonable request. [https://www.diw.de/en/diw\_01.c.601584.en/data\_access.html][1] [1]: https://www.diw.de/en/diw_01.c.601584.en/data_access.html