Fourth BNT162b2 vaccination neutralization of omicron infection after heart transplantation

We investigated changes in receptor-binding domain IgG and neutralizing antibodies against the omicron and delta variants, vs the wild-type virus, in response to a fourth BNT162b2 dose in 90 heart transplant (HT) recipients. The fourth dose induced anti-RBD IgG antibodies and a higher neutralization efficiency against the wild-type virus and the variants; however, neutralization efficiency against the omicron variant was lower than that against the delta variant (the latter demonstrating efficacy similar to that against the wild-type virus). Notably, while IgG anti-RBD antibodies were detectable in >80% of the HT recipients, only about half demonstrated neutralization efficiency against the omicron variant. A SARS-CoV-2-specific-T-cell response following the fourth dose was evident in the majority of transplant recipients. Boosting vulnerable groups improves antibody responses (including neutralizing responses) and cellular immunity, but the incomplete immunological response, particularly for omicron, suggests continued preventive measures and optimization of vaccination strategies that elicit strong, and long-lasting immune responses, in this high-risk population, should remain a priority.