Monitoring humoral and cellular immunity over 6 months after mRNA-based bivalent COVID-19 vaccine administration

The results of this study provide important insights on the duration of humoral and cellular protection in study participants who received the new bivalent mRNA COVID-19 vaccine formulation. Despite the pre-existing strong immunity acquired either by homologous vaccination or natural infection, the kinetics of total anti-SARS-CoV-2 antibodies and SARS-CoV-2 IGRA exhibited characteristics similar to those observed after the primary cycle of vaccination and subsequent booster doses of the previous monovalent mRNA COVID -19 vaccine formulation, with a peak followed by a gradual decline to 6 months after the bivalent booster dose. Notably, we demonstrated that both total anti-SARS-CoV-2 antibodies and anti-SARS-CoV-2 IGRA levels declined after six months, with the rate of study responders who had levels consistent with the postulated protective correlates being similar to or only slightly higher than the rates observed at baseline.