The Study of Antibody Response after Completing CoronaVac 2 Doses and Associated Factors of Antibody Response

Abstract

       Coronavirus disease 19 (COVID-19) has severely aff ected a lot of people globally; however, many vaccines have been developed to reduce the severity and mortality of patients with the disease The objectives of this study were to study the level of antibody response in adults after completing a two-dose regimen of CoronaVac, a COVID-19 vaccine, and the factors associated with antibody response. Antibody tests were randomly undertaken on annual check-up blood samples from 66 Lampang Hospital healthcare workers, who had received two doses of CoronaVac more than 4 weeks, for IgG antibodies to SARS-CoV-2 by using the SARS-CoV-2 IgG II Quant method and the ARCHITECH i1000 analyzer. The results showed that 100% of the participants after 4 weeks of two-dose vaccination had antibodies to SARS-CoV-2. The mean antibody level was 1,021.2 AU/mL with the minimum and maximum levels of 82.1 and 4,521.9 AU/mL, respectively. The mean antibody level of the subjects aged >45 years (723.7 AU/mL) was signifi cantly lower than in those aged ≤45 years (1,240.4 AU/mL, p = 0.0004). The mean antibody level of the subjects who had blood tests after vaccination for more than 50 days (664.2 AU/mL) was signifi cantly lower than those who had blood tests in ≤50 days (1,212.1 AU/mL, p = 0.0001). There was no signifi cant diff erence between the antibody levels in men and women (p > 0.05). In a conclusion, the antibody levels of >45-year-old subjects who had blood tests >50 days after receiving a second dose of CoronaVac had signifi cantly dropped. Therefore, a third dose of Covid-19 vaccine should be considered for this age group.