A study of anti-SARS-CoV-2 antibodies among healthcare personnel and the general population

Bulgaria, like many other countries, has experienced the far-reaching consequences of the Coronavirus disease 2019 (COVID-19) pandemic. Seroprevalence studies serve as a crucial method for assessing the exposure and immunity levels within a population. In this serosurvey, which is the first of this kind conducted in Bulgaria, we enrolled 104 healthcare workers (HCWs) from one front-line Bulgarian hospital and 237 individuals from the general population. Serum samples were collected in December 2021 from the general population and in February 2023 from HCWs and the general population. The presence of four anti-SARS-CoV-2 antibodies was evaluated: anti-Spike 1-IgG, anti-Nucleoprotein-IgG, anti-Spike1-IgA and anti-Recombinant binding domain neutralizing antibodies. Our results showed high percentages of seropositivity in both the HCWs and the general population (99% and 78%, respectively) in February 2023. HCWs had significantly higher mean IgA and mean anti-S1-IgG antibody levels compared to the general population. The seropositivity in the general population in December 2021 was 79%. The mean levels of IgA and anti-NCP-IgG were significantly higher, whereas the mean anti-S1-IgG levels were significantly lower in February 2023 compared to December 2021. We found a strong correlation between neutralizing antibodies and anti-S1-IgA and anti-S1-IgG antibodies for all tested groups. It is necessary to perform large-scale serosurveys to provide analysis of the seroprevalence in a larger population and its dynamics over time and to facilitate evidence-based strategies that will safeguard the health and well-being of the Bulgarian population and contribute to the global efforts in combating the COVID-19 pandemic.