SARS-CoV-2 seroprevalence in Germany - a population based sequential study in five regions

Gornyk, D.; Harries, M.; Gloeckner, S.; Strengert, M.; Kerrinnes, T.; Bojara, G.; Castell, S.; Frank, K.; Gubbe, K.; Heise, J.-K.; Hernandez, P.; Kappert, O.; Kern, W.; Illig, T.; Klopp, N.; Maass, H.; Ortmann, J.; Kessel, B.; Roller, G.; Schlueter, M.; Tonn, T.; Ziemons, M.; Kemmling, Y.; Lange, B.; Krause, G.

Prevalence of SARS-CoV-2 antibodies is an essential indicator to guide measures. Few population-based estimates are available in Germany. We determine seroprevalence allowing comparison between regions, time points, socio-demographic and health-related factors. MuSPAD is a sequential multi-local seroprevalence study. We randomly recruited adults in five counties with differing cumulative SARS-CoV-2 incidence July 2020 - February 2021. Serostatus was determined using Spike S1-specific IgG ELISA. We determined county-wise proportions of seropositivity. We assessed underestimation of infections, county and age specific infection fatality risks, and association of seropositivity with demographic, socioeconomic and health factors. We found seroprevalence of 2.4 % (95%CI: 1.8-3.1%) for Reutlingen in June 2020 (stage 1) which increased to 2.9% (95%CI: 2.1-3.8%) in October (stage 2), Freiburg stage 1 1.5% (95% CI: 1.1-2.1%) vs. 2.5% (95%CI: 1.8-3.4%), Aachen stage 1 2.3% (95% CI: 1.7-3.1%) vs. 5.4% (95%CI: 4.4-6.6%), Osnabrueck 1.3% (95% CI: 1.0-1.9%) and Magdeburg in Nov/Dec 2020. 2.4% (95%CI 1.9-3.1%). Number needed to quarantine to prevent one infection was 8.2. The surveillance detection ratio (SDR) between number of infections based on our results and number reported to health authorities ranged from 2.5-4.5. Participants aged 80+ had lower SDR. Infection fatality estimates ranged from 0.2-2.4%. Lower education was associated with higher, smoking with lower seropositivity. Seroprevalence remained low until December 2020 with high underdetection. The second wave from November 2020 to February 2021 resulted in additional 2-5% of the population being infected. Detected age specific differences of SDR should be taken into account in modelling and forecasting COVID-19 morbidity. Funding: The Helmholtz Association, European Union's Horizon 2020 research and innovation programme [grant number 101003480] and intramural funds of the Helmholtz Centre for infection (HZI).