Effect of Vaccination on Seroprevalence of COVID-19 among Blood donors - A cross-sectional Analytic Study from South India

India achieved impressive strides by providing 1.7 billion doses of the COVID-19 vaccine to more than 940 million people, attaining 100% first dose coverage and 80% overall immunization coverage as of February 9, 2022. Compared to unvaccinated individuals, vaccinated people have considerably decreased risks of infection, serious illness, hospitalization, and death. With the help of this study, we determined the prevalence of COVID-19 IgG antibodies with respect to vaccination. The cross-sectional analytical study was conducted from July 2021 to April 2022 on 809 healthy donors. All donor samples were screened for COVID-19 IgG antibodies against S1 protein using IgG ELISA kits (Qualisa COVID-19 IgG kits, Tulip, Goa, India). Data regarding COVID-19 infection history, vaccination status, type of vaccine, and the number of doses were obtained. All data were entered in Microsoft Excel and analyzed using SPSS version 21. Out of 809 blood donors, a total of 650 participants were vaccinated, among which 89.5% had COVID-19 IgG antibodies and 10.5% had no antibodies. Out of the 159 who had not taken vaccination, 52.8% of the participants had COVID-19 IgG antibodies, and 47.2% of the donors had no COVID-19 IgG antibodies. A total of 617 participants have taken the Covishield vaccine, of which 90.2% had COVID-19 IgG antibodies. A total of 32 donors have taken Covaxin, of which 78.1% had COVID-19 IgG antibodies. The above study has shown that COVID-19 vaccination enhances covid antibody formation, and multiple doses of vaccine ensure longevity of these antibodies.