Germany's low SARS-CoV-2 seroprevalence confirms effective containment in 2020: Results of the nationwide RKI-SOEP study

Pre-vaccine SARS-CoV-2 seroprevalence data from Germany are scarce outside hotspots, and socioeconomic disparities remained largely unexplored. The nationwide RKI-SOEP study with 15,122 adult participants investigated seroprevalence and testing in a supplementary wave of the Socio-Economic-Panel conducted predominantly in October-November 2020. Self-collected oral-nasal swabs were PCR-positive in 0.4% and Euroimmun anti-SARS-CoV-2-S1-IgG ELISA from dry capillary blood in 1.3% (95% CI 0.9-1.7%, population-weighted, corrected for sensitivity=0.811, specificity=0.997). Seroprevalence was 1.7% (95% CI 1.2-2.3%) when additionally adjusting for antibody decay. Overall infection prevalence including self-reports was 2.1%. We estimate 45% (95% CI 21-60%) undetected cases and analyses suggest lower detection in socioeconomically deprived districts. Prior SARS-CoV-2 testing was reported by 18% from the lower educational group compared to 25% and 26% from the medium and high educational group (p<0.0001). Symptom-triggered test frequency was similar across educational groups. However, routine testing was more common in low-educated adults, whereas travel-related testing and testing after contact with an infected person was more common in highly educated groups. In conclusion, pre-vaccine SARS-CoV-2-seroprevalence in Germany was very low. Notified cases appear to capture more than half of infections but may underestimate infections in lower socioeconomic groups. These data confirm the successful containment strategy of Germany until winter 2020.