Seroepidemiological Observational Study in Total and Neutralizing Antibodies to SARS-CoV-2 Among Primary Care...

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.

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.

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<0.001). Also, participants who were vaccinated and contracted the infection presented higher levels of anti-S antibodies compared to those who were unvaccinated and did not develop symptoms (471.10 vs. 83.27, p<0.001).

This population-based seroepidemiological study underscores the synergistic impact of vaccination and natural infection in sustaining elevated antibody levels during the Omicron period. The findings emphasize the importance of continuous immunological surveillance within primary healthcare settings to identify individuals at risk of declining immunization and to inform evidence-based booster vaccination strategies, thereby enhancing preparedness and resilience against future pandemic responses.