Quantitative Immunoglobulin G and Interferon-Gamma Responses After Different Booster Strategies of CoronaVac and BNT162b2 Vaccines in Türkiye.

Abstract

Objective: The global effort to combat the COVID-19 pandemic requires a comprehensive assessment of vaccine efficacy, including both humoral and cellular immune responses. This study aimed to determine the effects of CoronaVac and BNT162b2 booster doses on quantitative immunoglobulin G (IgG) and interferon-gamma (IFN-γ) responses of individuals primed with two doses of CoronaVac in Türkiye.

Materials and methods: This prospective cohort study included participants aged 18-59 years, without comorbidities, who were not under drug therapy and had no clinical history of COVID-19 and primed with CoronaVac. Participants were divided into three groups: Group 1 received a single CoronaVac booster, Group 2 received a single BNT162b2 booster, and Group 3 received two BNT162b2 boosters. Humoral immunity was assessed by the determination of IgG levels against the spike receptor-binding domain (RBD) protein of SARS-CoV-2, and cellular immunity was assessed by the IFN-γ release assay.

Results: The study included 48 participants. When the 6-12-month post-vaccination period was considered, the lowest quantitative IgG levels were detected in Group 1. Higher IgG levels were detected in Group 2 and Group 3, with Group 3 revealing the highest levels for both IgG and IFN-γ responses. Although the differences between the IFN-γ levels among the three groups were not statistically significant, the individuals boosted with the BNT162b2 demonstrated two- and three-fold higher levels compared to the homologous boosted individuals. The median IgG and IFN-γ values were significantly higher in the younger participants compared to the older participants in Group 3.

Conclusion: Our findings revealed that although homologous and heterologous boosting in inactivated vaccine-primed individuals provided effective humoral and cellular immunity, boosting with two doses of BNT162b2 should be prioritized since it exhibited a positive impact on both humoral and cellular immunity.