Evaluation of the immune response to COVID-19 vaccine mRNA BNT162b2 and correlation with previous COVID-19 infection

BACKGROUND: The kinetics of immune response after vaccination with mRNA-BNT162b2 (Comirnaty®) and the correlation with previous COVID-19 infection are still unclear. METHODS: Thirty-six subjects receiving mRNA-BNT162b2 were prospectively studied [10 days after the first dose (Time 1), 7 days and 16 weeks after the second dose (Time 2 and Time 3)] to determine antibody titers against nucleocapside, trimeric spike protein (TSP) and receptor-binding-domain (RBD) of the spike protein. Ten subjects had a previous COVID-19 infection not requiring hospitalization (Group 1) and 26 did not (Group 2). RESULTS: At Time 1 all subjects in Group 1 had IgG against TSP > 800 AU/mL compared to 11/26 (42.3%) in Group 2, whilst at Time 2 all subjects in both groups had > 800 AU/mL. The mean IgG against TSP titer at Time 3 was 711 AU/mL (95% CI 652–800) in Group 1 and 240 AU/mL (95% CI 112–375) in Group 2 (p < 0.0001). However, all subjects in both groups maintained antibody titers above the lower threshold limit at each time-point considered. These results were confirmed also using anti-RBD antibodiy tests. Antibodies against nucleocapside were reactive only in subjects in Group 1 and remained stable during the study period. No subject had a new onset of COVID-19 infection within 16 weeks of follow-up. CONCLUSIONS: Subjects with previous COVID-19 infection have a more rapid immune response to mRNA-BNT162b2 than others and maintained higher antibody titers during 16 weeks of follow-up. However, no new COVID-19 infection also in subjects with lower antibody titers.