Antibody Response After Two Doses of Inactivated SARS-CoV-2 Vaccine in Healthcare Workers with and without Previous COVID-19 Infection: A Prospective Observational Study

Abstract

In this study, we aimed to investigate the anti-S1 IgG response that occurs after inactivated severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) vaccine and the factors affecting this response in healthcare workers (HCWs) who are in the risk group for coronavirus disease 2019 (COVID-19). A total of 276 HCWs, of whom 82 previously exposed to COVID-19 infection and 194 naive who are working in Kafkas University Faculty of Medicine, Health Research and Application Center were included in this study. Anti-SARS-CoV-2 QuantiVac ELISA IgG (Euroimmun, Lubeck, Germany) kit, coated with recombinant S1 antigen including the receptor binding domain of the SARS-CoV-2 S protein was used for quantitative determination of the humoral immune response in serum samples 28 days after the first and second dose of vaccination. The antibody responses and the mean antibody levels of 194 naive HCWs 28 days after the first and second doses of vaccine were determined to be 27.2%, 98.5% and 19.72 ± 38.73 BAU, 222.09 ± 119.18 binding antibody unit (BAU), respectively. The mean antibody levels of 82 HCWs previously exposed to COVID-19 infection 28 days after the first and second doses of vaccine were 268.27 ± 112.91 BAU and 309.45 ± 112.75 BAU, respectively. The antibody response reached 100% after the first dose of vaccination. A statistically significant difference was observed between the antibody levels after the first and second doses of vaccine in both groups (p< 0.001). It was determined that the mean antibody level formed after the first dose of vaccine administration of HCWs who had COVID-19 infection was statistically higher than the mean antibody level formed after the second dose of vaccine in naive individuals (p= 0.003). There was no significant difference in mean antibody levels after the first (269.10 ± 117.24 BAU and 266.59 ± 105.65 BAU, respectively) and second doses (309.98 ± 113.17 and 308.36 ± 114.04 BAU, respectively) between individuals previously exposed to COVID-19 infection in the last three months and more than three months (p= 0.925 and p= 0.951, respectively). The highest antibody levels were detected in the 19-30 age group (251.50 ± 119.81 BAU), women (249.03 ± 118.57 BAU), body mass index (BMI)< 20 kg/m2 group (267.08 ± 137.51) and non-smokers (237.85 ± 124.83 BAU) in naive HCWs after the second dose of vaccination. A statistically significant difference was found between age, gender, BMI, smoking and vaccine response (p= 0.003, p= 0.005, p= 0.008 and p= 0.036, respectively). The post-vaccination adverse effects after the first and second doses of vaccination were not observed in 76.1% and 73.9% of HCWs, respectively. There was no increase in the frequency of post-vaccination adverse events after the first and second doses in individuals previously exposed to COVID- 19 infection and naive persons (p= 0.46 and p= 0.43, respectively). It was determined that the mean antibody level after the first dose of vaccination in HCWs previously exposed to COVID-19 infection was higher than naive individuals after the second dose vaccination. Prospective clinical studies on antibody levels and their duration of protection are needed for the prevention of COVID-19 infection.