Prevalence of anti-SARS-CoV-2 antibodies in Poznań, Poland, after the first wave of the COVID-19 pandemic

In comparison to other European countries, during the first months of COVID-19 pandemic, Poland reported relatively low number of confirmed cases of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections. To estimate the scale of pandemic in Poland, a serosurvey of antibodies against SARS-CoV-2 was performed after the first wave of COVID-19 in Europe (March – May 2020). Within this study, we collected samples from July 28 to September 24, 2020 and based on the ELISA results, we found that 1.67% (25/1500, 95%CI 1.13 - 2.45) of the Poznan (Poland) metropolitan area’s population had antibodies against SARS-CoV-2 after the first wave of COVID-19. However, the presence of anti-SARS-CoV-2 IgG antibodies was confirmed with immunoblot in 56% (14/25) samples, what finally resulted in decrease of seroprevalence, i.e. 0.93% (14/1500, 95%CI 0.56 - 1.56). The positive anti-SARS-CoV-2 IgG results were associated with age, occupation related to constant contact with people, travelling abroad, non-compliance with epidemiological recommendations and direct contact with the novel coronavirus. Our findings confirm the low SARS-CoV-2 incidence in Poland and imply that the population had little herd immunity heading into the second and third wave of the pandemic, and therefore herd immunity contributed little to prevent the high numbers of SARS-CoV-2 infections and COVID-19 related deaths in Poland during these subsequent waves.