Sex, Age, and Previous Herpes Zoster Infection Role on Adverse Events Following Immunization with Adjuvanted Recombinant Vaccine.

Adverse events following immunizations (AEFIs) with recombinant zoster vaccine (RZV) are underexplored in fragile populations. This study aims to assess incidence, duration, and characteristics of AEFIs, focusing on the impact of sex, age, and prior Herpes Zoster (HZ) infection in a frail population, including solid organ transplant recipients. We conducted an observational study on patients receiving RZV, and AEFIs were classified as local or systemic and analyzed for incidence, duration, and patterns across groups. We showed that females had a higher incidence of AEFIs (p = 0.02), both local and systemic symptoms, such as swelling +/- redness at the site of injection and fatigue, after the first and second doses. Younger adults experienced more systemic reactions, while older adults reported more local events (e.g., redness and swelling, p = 0.01). Moreover, patients with previous HZ infection exhibited a higher incidence of AEFIs after the second dose (68% vs. 38%, p = 0.001). In conclusion, sex, age, and clinical history significantly influenced AEFI incidence and manifestations. Therefore, it is important to personalize vaccination strategies in frail populations, by tailored administration and monitoring plans, especially in females and individuals with prior HZ infection, to improve vaccine safety and patient outcomes.