Prevalence of SARS-CoV-2-specific antibodies in a sample of the Lithuanian population-based study in Spring 2023

Objectives Despite positive trends in SARS-CoV-2 epidemiology, seroprevalence surveys remain an important tool for estimating the magnitude of the COVID-19 pandemic. This study aimed to investigate the prevalence of IgG antibodies against SARS-CoV-2 nucleocapsid (N) and spike (S) proteins in a sample of the Lithuanian population (N=517) and evaluate how the pattern of seropositivity correlates with the levels of SARS-CoV-2 infection and vaccination. Methods Study participants (aged 18-88 years) filled in the questionnaire self-reporting their demographic-social variables, health status, and SARS-CoV-2-related status. The anti-S and anti-N IgG levels were estimated using a microarray ELISA test. Results After several pandemic waves and vaccination campaign, the seroprevalence of SARS-CoV-2-specific IgG in the analyzed sample was 97.87% by March-May, 2023. We determined the 96.91% prevalence of anti-S and 58.03% prevalence of anti-N IgG. The majority of study participants (71.18%) had hybrid immunity induced by vaccination and SARS-CoV-2 infection. 20.3% of study participants were anti-N IgG positive without reporting any previous symptoms or a positive SARS-CoV-2 test. A decline of anti-N IgG positivity within 9 months after infection was observed. Conclusions This study demonstrates high total seroprevalence in March-May 2023 in all age groups indicating a widely established humoral immunity against SARS-CoV-2 in Lithuania.