Antibody response after a booster dose of BNT162B2mRNA and inactivated COVID-19 vaccine.

Introduction: The necessity of a booster dose is a matter that has not been as yet illuminated, although it is noted that neutralizing antibody titers decrease over time. We aimed therefore to evaluate antibody titers and seroconversion rates after a booster mRNA vaccine and a booster inactivated vaccine. Methods: A total of 322 participants were divided into three main groups, with two subgroups each, based on their vaccinations and previous infection history. The levels of anti-SARS-CoV-2 Ig-G were analyzed with the Elecsys® Anti-SARS-CoV-2 S assay. Results: The antibody titers showed a linear and significant increase from one vaccine group to the other, displaying progressive changes from group 2IV to group 3IV, and then to group 2IV/mRNA. All of the seronegative participants were in the 2IV(-) subgroup; 93.3% of the participants whose antibody titers were above the upper limit were in the 2IV/mRNA group. Doctors were much more inclined to have a booster dose and mRNA vaccines than nurses. The status of being a doctor increases the rate of having a booster dose 7.8 times; likewise, each annual increase in age increases the rate 1.05 times. Conclusion: Anti-SARS-CoV-2 IgG levels decrease over time. The antibody response rate to only two doses of the inactivated vaccine was meager, so a booster dose is necessary to maintain the effectiveness of inactivated vaccines. The third dose of the vaccine, especially that of the mRNA vaccine, which was found to be much more superior to the inactivated vaccine, should be strongly recommended.