Human IgM and IgG Responses to an Inactivated SARS-CoV-2 Vaccine

Objective:The ongoing COVID-19 pandemic warrants accelerated efforts to test vaccine candidates.To explore the influencing factors on vaccine-induced effects,antibody responses to an inactivated SARS-CoV-2 vaccine in healthy individuals who were not previously infected by COVID-19 were assessed.Methods:All subjects aged 18-60 years who did not have SARS-CoV-2 infection at the time of screening from June 19,2021,to July 02,2021,were approached for inclusion.All participants received two doses of inactivated SARS-CoV-2 vaccine.Serum IgM and IgG antibodies were detected using a commercial kit after the second dose of vaccination.A positive result was defined as 10 AU/mL or more and a negative result as less than 10 AU/mL.This retrospective study included 97 infection-naive individuals(mean age 35.6 years;37.1%male,62.9%female).Results:The seropositive rates of IgM and IgG antibody responses elicited after the second dose of inactivated SARS-CoV-2 vaccine were 3.1%and 74.2%,respectively.IgG antibody levels were significantly higher than IgM levels(P<0.0001).Sex had no effect on IgM and IgG antibody response after the second dose.The mean anti-IgG level in older persons(≥42 years)was significantly lower than that of younger recipients.There was a significantly lower antibody level at>42 days compared to that at 0-20 days(P<0.05)and 21-31 days(P<0.05)after the second dose.Conclusion:IgG antibody response could be induced by inactivated SARS-CoV-2 vaccine in healthy individuals(>18 years),which can be influenced by age and detection time after the second dose of vaccination.