Seroprevalence of SARS-CoV-2 antibodies in the county town of Slovakia - a pilot study from the Trencin city.

Slovakia is a country with only 5.45 million inhabitants. However, the past two years of the COVID-19 pandemic have shown huge inter-regional differences. These were represented by different numbers of diagnosed SARS-CoV-2 cases and the vaccination rates in the regions, as well as by the willingness of the inhabitants to comply with anti-pandemic measures or to undergo testing. The occurrence of such regional disparities provided a rational basis for monitoring the epidemic situation within smaller areas, e.g. at city level. Trencin is a medium-sized Slovak county town with about 55 000 inhabitants. The city administration gave its residents the opportunity to assess their current level of antibodies against the SARS-CoV-2 virus, and received an additional benefit in the form of data on the real epidemic situation in the city, which helped in further management of anti-pandemic measures. The primary aim of the study, conducted in January and February 2022, was to determine the levels of antibodies against the SARS-CoV-2 virus in the inhabitants of Trencin. The results showed that 75% of the study participants, representing the adult population of the city, had detectable IgG antibodies against the SARS-CoV-2 spike protein. Noteworthy, at the time of the study, 13% of the Trencin city population who were unaware of overcoming COVID-19 had specific antibodies against the virus. Furthermore, the antibody levels in recovered unvaccinated subjects increased not only with the severity of their COVID-19 symptoms, but also after multiple recoveries from the disease. On the other hand, the severity of side effects after vaccination did not influence the antibody levels. The results of the study are in line with the current view that hybrid immunity (vaccination plus SARS-CoV-2 infection in any order) offers greater protection than immunity elicited by vaccination or COVID-19 separately. Keywords: SARS-CoV-2 coronavirus; COVID-19; ELISA; seroprevalence; antibodies; vaccination.

Seroprevalence of SARS-CoV-2 IgG antibodies in the staff of the Slovak Academy of Sciences in response to COVID-19 and/or vaccination: situation in August 2021.

Cross-sectional seroprevalence study of SARS-CoV-2 IgG antibodies was accomplished in the Slovak Academy of Sciences to inform authorities of research institutions about the situation at their workplaces, to assess the risk of next exposure to SARS-CoV-2, and to guide decisions on institutional measures sustaining essential research in evolving epidemic situation. Study participants provided informed consent, anamnestic information, and self-collected dry blood spot samples that were analyzed by ELISA for SARS-CoV-2 S protein-specific IgG antibodies. Relative antibody levels detected in 1928 subjects showed seroprevalence of 84.13% and led to the following main findings consistent with the current knowledge: (1) mRNA-based vaccines induce better humoral response compared to adenovirus vaccines, (2) antibody levels reflect severity of COVID-19 symptoms, (3) post-COVID vaccination results in marked elevation of IgG levels particularly in asymptomatic and mild cases, (4) antibody levels decrease with increasing time elapsed from vaccination or COVID-19. In addition, data sorting to distinct research institutes and their clustering to three principal scientific sections of the Slovak Academy of Sciences revealed marked differences in seroprevalence, and allowed to identify workplaces with relatively high seropositivity and response rate that can potentially provide a safer working environment than those, where seroprevalence was low or unknown due to low participation. Thus, findings of this study can have direct implications on management decisions during the next pandemic development, with the necessity to keep in mind the phenomenon of time-dependent immunity waning and current spread of more contagious Delta variant of SARS-CoV-2. Keywords: SARS-CoV-2 coronavirus; COVID-19; spike protein; seroprevalence; antibodies; vaccination.