coronavac at first and 3months, unpaired nonparametric test, Wilcoxon ranksum (MannWhitney) test was performed. were measured by ELISpot assay. == Results == We found a 3.38fold increase in neutralizing antibody geometric mean titers (NA GMT, 78.69) 1 month after BNT booster and maintained at the third month (NA GMT, 80). Nevertheless, in the CV booster group, significantly lower NA GMT than BNT after 1 month and 3 months were KIT observed (21.44 and 28.44, respectively) (p< .001). In the ELISpot assay, IL2 levels after BNT were higher than baseline and CV booster (p< .001) while IFN levels were significantly higher than baseline (p< .001). The CD8+CD38+CD69+ and CD4+CD38+CD69+ T cells were stimulated predominantly in the third month of the BNT boosters. == Conclusion == The neutralizing antibody levels after 3 months of the BNT booster were higher than the antibody levels after CV in fully vaccinated individuals. On the contrary, ratio of the effector T cells increased along with greater IFN activation after BNT booster. By considering the waning immunity, we suggest a new booster dose with BNT for the countries that already had two doses of primary CV regimens. Keywords:SARSCoV, T cells, vaccines This study determines the effects of BNT162b2 (BNT) and CoronaVac (CV) boosters on the humoral and cellular immunity of individuals who had two doses of CV vaccination. The neutralizing antibody levels after 3 months of the BNT booster are higher than the antibody levels after CV in fully vaccinated individuals. The ratio of the effector T cells increases along with greater IFN activation after BNT booster. == Abbreviations == geometric mean titer peripheral blood mononuclear cells plaque reduction neutralization test spot forming units == 1. INTRODUCTION == The worldwide use of effective and safe COVID19 vaccines is still a high priority to control the pandemic and to (R)-Baclofen reduce the burden of COVID19. The vaccine type and vaccination schedule affect many of the cellular and molecular elements of innate and adaptive immune systems. Estimation of the immune responses after SARSCoV2 vaccinations is one of (R)-Baclofen the important parameters in order to predict the efficacy of booster vaccines. Therefore, testing the effectiveness of COVID19 vaccines in different vaccination schedules is necessary as there are a variety of vaccine availabilities, worldwide. Following primary vaccination, antibody and Tcell responses have decreased over time.1A booster dose being administered 6 months after the second dose of various vaccines significantly increased neutralizing antibody concentrations.2The heterologous vaccine regimens were reported to stimulate neutralizing antibodies more than the homologous vaccine protocols.3 In Turkey, the inactivated vaccine CoronaVac (Sinovac Life Sciences) was the first vaccine to receive approval by the Ministry of Health. Healthcare workers and individuals over the age of 65 were suggested two doses of CV administered 2 months apart in the initial phase of the vaccination program.4After 6 months, the Ministry of Health of Turkey recommended a booster of BNT as an alternative option to the CV booster. In early studies of the CV, effectiveness after twodose schedules was reported as 60%90%.4,5Nevertheless, these studies were performed approximately 6 weeks after the second dose. Six months after the second dose of CV, neutralizing antibody titers declined below the seropositivity cutoff value while a remarkable increase in the neutralizing antibody concentrations was observed with the administration of a third dose.6However, our knowledge on the humoral and cellular immune responses obtained by BNT and CV boosters following two doses of primary CoronVac vaccination is still limited. In this study, we aimed to explore the neutralizing antibody and Tcell responses after the booster doses of CV and BNT following two doses of CV. == 2. MATERIALS AND METHODS == == 2.1. Study design and participants == The study was (R)-Baclofen conducted in three centers (Ko University Hospital, Istanbul University Cerrahpasa Hospital, and Istanbul University,.
