Background: Dynamics of antibody responses were investigated after a SARS-CoV-2 outbreak in a private company during the first wave of the pandemic.
Methods: Workers of a sewing company (Lithuania) with known SARS-CoV-2 RT-PCR result during the outbreak (April 2020) were invited to participate in the study. Virus-specific IgG and IgM were monitored 2, 6 and 13 months after the outbreak via rapid IgG/IgM serological test and SARS-CoV-2 S protein-specific IgG ELISA.
Results: Six months after the outbreak, 95% (CI 86-99%) of 59 previously infected individuals had virus-specific antibodies irrespective of the severity of infection. One-third of seropositive individuals had virus-specific IgM along with IgG indicating that IgM may persist for 6 months. Serological testing 13 months after the outbreak included 47 recovered individuals that remained non-vaccinated despite a wide accessibility of COVID-19 vaccines. The seropositivity rate was 83% (CI 69-91%) excluding one case of confirmed asymptomatic reinfection in this group. Between months 6 and 13, IgG levels either declined or remained stable in 31 individual and increased in 7 individuals possibly indicating an exposure to SARS-CoV-2 during the second wave of the pandemic.
Conclusions: Detectable levels of SARS-CoV-2-specific antibodies persist up to 13 months after infection for the majority of the cases.
Keywords: IgG/IgM dynamics; SARS-CoV-2; longitudinal study; serological monitoring.