COVID-19 Infection, Vaccination, and Antibody Levels: Investigating Correlations through a Cohort Study

Aim: The objective of this study was to explore the potential correlation between COVID-19 infection or vaccination and levels of anti-nucleocapsid (anti-N) and anti-spike (anti-S) antibodies. Methods: Among 6050 healthcare workers at the Ege University Hospital, a cohort study with 162 participants divided into three arms with 54 participants each was conducted. The three groups were selected as follows: those diagnosed with COVID-19 and not vaccinated (group 1), those diagnosed with COVID-19 and subsequently vaccinated with CoronaVac (group 2), and those not diagnosed with COVID-19 but vaccinated with two doses of CoronaVac (group 3). Antibody levels measured at the sixth month of follow-up were defined as the primary outcome. Results: At the sixth month, all serum samples tested positive for anti-S. Anti-S levels were found to be significantly higher in group 2 than in the other groups (p < 0.001). There were no differences in antibody levels between groups 1 and 3 (p = 0.080). Average antibody levels were found to be lower in office workers and males. Anti-N antibodies were found to be positive in 85.1% of subjects at the sixth month. In group 2, anti-N antibodies were detected in all samples at the sixth month. Anti-N antibody levels were not significantly different between groups 1 and 2 (p = 0.165). Groups 1 and 2 had significantly higher antibody levels than group 3 (p < 0.001). Conclusions: Vaccination or infection provide protection for at least 6 months. Those who have previously been diagnosed with COVID-19 do not need to be vaccinated in the early period before their antibody levels decrease.