Comparison between the homologous BNT162b2 and the heterologous Gam-COVID-Vac/BNT162b2 vaccine regimen in republic of North Macedonia

The medical and socio-economic consequences that stemmed from the COVID-19 pandemic, forced the healthcare policymakers in Republic of North Macedonia to rely on five different vaccines against the SARS-CoV-2 virus, in order to reach a satisfactory level of herd immunity. It is here where we got the idea to compare the heterologous Gam-COVID-Vac/BNT162b2 regimen to the homologous BNT162b2 regimen, with our main focus being the immunogenicity differences between the two of them. Additionally, we researched the variation in humoral immune response relative to age strata; the reactogenicity differences; and discrepancies in SARS-CoV-2 infection incidence between the two regimens. To achieve this, antibody titers in sera samples from fifty-three (53) healthcare workers, divided in heterologous and homologous group, were analysed at six different time checkpoints. Our results showed robust immunogenic response after the administration of the booster dose (4. 2-fold increase in antibody titers), followed by a slower-waning humoral immune protection in the heterologous regimen, compared to the homologous BNT162b2 schedule, furthermore confirmed by non-inferiority testing (Geometric Mean Ratio=0,98) at the final checkpoint. That, coupled with the similar reactogenicity (p=0,767) of both regimens, imply that the Gam-COVID-Vac/BNT162b2 combination might be a feasible approach in the effort to contain the COVID-19 pandemic.