Seroepidemiological Observational Study in Total and Neutralizing Antibodies to SARS-CoV-2 Among Primary Care Patients in Crete, Greece

Background/Aim: The current study aimed to assess the levels of total IgG antibodies against the spike (S) and nucleocapsid (N) proteins of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) as well as the neutralizing antibodies (nAbs) in a population of Crete, Greece. Patients and Methods: In total, 1,061 participants with 2,081 follow-up measurements during May-December 2022, from eight different primary healthcare facilities, were categorized into four groups, based on vaccination and illness status. Blood samples were collected and processed to measure anti-S, anti-N and neutralizing antibodies. Based on specific cutoff values and using non-parametric methods, antibody levels were compared between different categories or disease/vaccination of SARS-CoV-2. Results: The proportion of participants who had been infected was higher among the unvaccinated. Additionally, an increase in the number of vaccine doses administered resulted in a noteworthy reduction in the frequency of illness, with proportions decreasing from 69.2% among those who were not vaccinated or 83.1% among those vaccinated 1-2 times to 21.6% among those vaccinated 4+ times (p