A longitudinal seroprevalence study in a large cohort of working adults reveals that neutralising SARS-CoV-2 RBD-specific antibodies persist for at least six months independent of the severity of symptoms

Wagner, A.; Guzek, A.; Ruff, J.; Jasinska, J.; Scheikl, U.; Zwazl, I.; Kundi, M.; Stockinger, H.; Farcet, M. R.; Kreil, T.; Hoeltl, E.; Wiedermann, U.

Background In spring 2020, at the beginning of the first pandemic severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) wave in Europe, we set up an assay system for large-scale testing of virus-specific and protective antibodies including their longevity. Methods We analysed the sera of 1655 adult employees for SARS-CoV-2-specific antibodies using the S1 subunit of the spike protein of SARS-CoV-2. Sera containing S1-reactive antibodies were further evaluated for receptor-binding domain (RBD)- and nucleocapsid protein (NCP)-specific antibodies in relation to the neutralisation test (NT) results at 0, three and six months. Findings We found immunoglobulin G (IgG) and/or IgA antibodies reactive to the S1 protein in 10.15% (n=168) of the participants. In total, 0.97% (n=16) were positive for S1-IgG, 0.91% (n=15) were S1-IgG- borderline and 8.28% (n=137) exhibited only S1-IgA antibodies. Next, we evaluated the 168 S1-reactive sera for RBD- and NCP specificity: 8.33% (n=14) had detectable RBD-specific and 6.55% (n=11) NCP-specific antibodies. The latter correlated with NTs (kappa coefficient = 0.8660) but started to decline already after 3 months. RBD-specific antibodies correlated best with the NT (kappa = 0.9448) and only these antibodies were stable for up to six months. All participants with virus-neutralising antibodies reported symptoms, of which, anosmia and/or dysgeusia correlated best with the detection of virus-neutralising antibodies. Interpretation RBD-specific antibodies were most reliably detected post infection, independent of the number/severity of symptoms, and correlated best with protective neutralising antibodies at least for six months. They thus qualify best for large-scale seroepidemiological evaluation of both seroprevalence and seroprotection.