XBB 1.5 monovalent booster vaccination stimulates oral mucosal and systemic immune responses in healthy adults

The XBB1.5 monovalent vaccine boosts neutralizing antibody levels in blood and mucous membranes, with the largest increase observed against the XBB1.5 variant. This likely reflects the enhancement of cross-reactive antibodies influenced by prior exposure and hybrid immunity, rather than the production of entirely XBB1.5-specific responses. Improved oral mucosal immune responses may reduce the risk of COVID-19 infection and severe illness.