Immunogenicity of BNT162b2 and CoronaVac boosters in fully vaccinated
individuals with CoronaVac against SARS-CoV-2: A Longitudinal Study
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.