Objective: There is a need for the immunogenicity of different boosters after widely used inactivated vaccine regimens. We aimed to determine the effects of BNT162b2 and CoronaVac boosters on the humoral and cellular immunity of individuals who had two doses of CoronaVac vaccination. Methods: The study was conducted in three centers (Koc University Hospital, Istanbul University Cerrahpasa Hospital, and Istanbul University, Istanbul Medical School Hospital) in Istanbul. Individuals who had two doses of CoronaVac and no history of COVID-19 were included. The baseline blood samples were collected three to five months after two doses of CoronaVac. Follow-up samples were taken one and three months after third doses of CoronaVac or one dose of mRNA BNT162b2 boosters. Neutralizing antibody titers were detected by plaque reduction assay. T cell responses were evaluated by Elispot assay and flow cytometry. Results: We found a 3.38-fold increase in neutralizing antibody titers (Geometric Mean Titer [GMT], 78.69) one month after BNT162b2 booster and maintained at the three months (GMT, 80). However, in the CoronaVac group, significantly lower GMTs than BNT162b2 after 1 month and 3 months (21.44 and 28.44, respectively) indicated the weak immunogenicity of the CoronaVac booster (p<0.001). In the ELISpot assay, IL-2 levels after BNT162b2 were higher than baseline and CoronaVac booster (p<0.001) and IFN-γ levels were significantly higher than baseline (P<0.001). The CD8+CD38+CD69+ and CD4+CD38+CD69+ T cells were stimulated significantly at the 3 rd month of the BNT162b2 boosters. Conclusion: The neutralizing antibody levels after three months of the BNT162b2 booster were higher than the antibody levels after CoronaVac. On the other hand, specific T cells might contribute to immune protection. By considering the waning immunity, we suggest a new booster dose with BNT162b2 for the countries that already have two doses of primary CoronaVac regimens.