A longitudinal study depicted that in people previously fully vaccinated with CoronaVac against coronavirus disease, the extent of post BNT162b2 (BNT) booster responses was greater than CoronaVac (CV) booster. Zeynep Ece Kuloğlu et al. aimed to assess the impact of CV and BNT boosters on cellular and humoral immunity of people who were administered 2 doses of CV vaccination.

People with no history of SARS-CoV-2 infection and who were formerly immunized with 2 doses of CV were incorporated. The collection of baseline blood samples was done following the second CV dose. Follow-up blood samples were acquired one and three months post-administration of one dose of BNT boosters, or third doses of CV. Utilizing the plaque reduction assay, measurement of neutralizing antibody titers was done.

With the use of flow cytometry, the ratios of effector CD8+CD38+CD69+ T cell, effector CD4+CD38+CD69+ T cell, and CD4+ T cell, CD8+ T cell were explored. The measurement of intracellular interleukin-2 (IL-2) and interferon-gamma (IFN-γ) responses was done using ELISpot assay. Notably, a 3.38-fold elevation in neutralizing antibody geometric mean titers (NA GMT, 78.69) was observed one month post BNT booster and maintained in the 3rd month (NA GMT, 80), as shown in Figure 1:

Compared to the BNT booster group (NA GMT, 28.44), a substantially reduced NA GMT was seen in the CV booster group (NA GMT, 21.44) after 1 month and 3 months. The levels of IL-2 were greater than baseline and CV booster while levels of IFN-γ were remarkably greater than baseline in the ELISpot assay. The CD8+CD38+CD69+ and CD4+CD38+CD69+ T cells were exhilarated primarily in the 3rd month of the BNT boosters.

Following the BNT booster, the effector T cells ratio elevated together with higher IFN-γ activation. To conclude, taking into account the declining immunity, in people who already received 2 doses of primary CV regimens, a new booster dose with BNT is suggested.