Immune Response to SARS-CoV-2 XBB.1.5 and JN.1 Variants Following XBB.1.5 Booster Vaccination in Liver Transplant Recipients.

BACKGROUND/OBJECTIVES: The efficacy of monovalent BNT162b2 Omicron XBB.1.5 booster vaccination in liver transplant recipients (LTRs) has yet to be described, particularly regarding the immune response to emerging variants like JN.1.

METHODS

This study evaluated humoral and cellular immune responses in 34 liver transplant recipients (LTRs) with varying SARS-CoV-2 immune histories before and after receiving a BNT162b2 Omicron XBB.1.5 booster vaccination. The assessment involved variant-specific serology, pseudovirus neutralization tests, and Interferon-γ release assays.

RESULTS

Participants had a median of four prior vaccinations, with 91.2% having a history of infection. Post-vaccination, significant increases in both Wuhan anti-S and Omicron-specific IgG antibodies and improved neutralization of B.1, XBB.1.5, and JN.1 pseudovirus particles were observed. Also, T-cell responses significantly increased post-vaccination. However, 17.6% of LTRs had no neutralizing antibodies against XBB.1.5 and JN.1, while 100% of healthy controls did. Shortly after vaccination, 18% of patients developed mild COVID-19. These LTRs had particularly low immune responses at baseline.

CONCLUSIONS

The monovalent XBB.1.5 booster improved overall SARS-CoV-2-specific immunity. However, some LTRs still showed low or undetectable immune responses, indicating that ongoing monitoring and further booster doses are necessary in this high-risk group.