Effect of btn162b2 and coronavac boosters on cellular immunity of individuals previously fully vaccinated with coronavac against sars-cov-2: a longitudinal study

In Turkey, 2 doses of inactivated vaccine (CoronaVac) were first used to protect from COVID-19. Then, to boost immunity, one dose of mRNA vaccine (BioNTech) or one dose of inactivated vaccine (CoronaVac) was administered. This study aimed to evaluate the cellular immunity developed against SARS-CoV-2 after 2 doses of CoronaVac and one dose of BioNTech or CoronaVac boosters. In this study, 33 individuals who are vaccinated with 2 doses of CoronaVac and had no history of Covid-19 were recruited. The study population was divided into 2 groups: Group A, individuals who received 2 doses of CoronaVac and a dose of Pfizer/BioNTech (n=27). Group B, 2 doses of CoronaVac and 1 dose of CoronaVac (n=6). Blood samples were collected 3-5 months after 2 doses of CoronaVac and 1 month after the 3rd dose of either Pfizer/BioNTech or CoronaVac. In the assessment of CD4+cell and CD8+ cell ratios after stimulation with a mixture of spike peptides, there were no significant changes in the magnitude of CD4+ and CD8+ T cells after BNT162b2 and CV boosters compared to baseline levels. The median ratio of effector CD8+CD38+CD69+ T cells and CD4+CD38+CD69+ T cells after 2 doses of CoronaVac were 1.160 and 4.375 respectively. There was no significant difference compared to baseline levels whereas a significant increase was detected in the 3rd month in effector CD8+CD38+CD69+and CD4+CD38+CD69+ T cells. The magnitude of BNT162b2 booster T cell responses was significantly higher than the CoronaVac booster. Thus, increased IFN-γ and IL-2 reactivity after the BNT162b2 booster, accompanied by an increase in effector CD8+CD38+CD69+T cells were detected. The ratio of effector CD4+CD38+CD69+ cells was also high in the 3rd month of the BNT162b booster.