B Cell Subtypes in Individuals Received mRNA or Inactivated Vaccine Boosters After Fully Vaccinated with CoronaVac: A Longitudinal Study.

In this study, we aimed to investigate the changes in the B cell subpopulations after homologous or heterologous COVID-19 boosters. Blood samples were collected after baseline (3-5 months after two doses of CoronaVac), 1 and 3 months after BNT162b2 (n=28 and n=6), and CoronaVac (n=7 and n=4) boosters. Peripheral blood mononuclear cells (PBMCs) were isolated and stained with B cell markers, the ratios of naïve (CD19+CD20+CD27-), memory (CD19+CD20+CD27+), memory B cells expressing IgG (CD19+CD20+CD27+IgG+), and effector memory B cells (CD19+CD20+CD27+CD38+) were identified with flow cytometry. Significantly higher expression of memory B cells was observed in one month with BNT162b2 (12.16% one month, 5.98% three months) and CoronaVac (14.18% one month, 9.00% three months) boosters. IgG expressing memory B cell expression was significantly higher with BNT162b2 than with CoronaVac booster in one month (22.70% and 13.95%, respectively). The ratio of effector B cells in the first month after CoronaVac booster (25.44%) was significantly higher than the BNT162b2 booster (9.90%, p =0.0263).