Long-term protection and response to a booster dose after primary hepatitis B vaccination in people under pre-exposure prophylaxis for HIV infection.

BACKGROUND

Universal hepatitis B virus (HBV) vaccination was introduced in Italy in 1991. However, the long-term durability of vaccine-induced protection remains under debate, particularly among high-risk groups such as men who have sex with men (MSM) using HIV pre-exposure prophylaxis (PrEP). This study aimed to assess HBV seroprotection and the immune response to a booster vaccine nearly 30 years after infant immunization among MSM-PrEP users.

SETTING

This retrospective study included Italian MSM using PrEP under 35 years of age in Milan, Italy, between 2017 and 2024.

METHODS

HBV serological status was determined at the start of PrEP. Participants with HBsAb levels below 10 mIU/mL were offered a booster dose. Statistical analyses were performed to compare demographic and clinical variables according to seroprotection status and booster response.

RESULTS

Overall, among 447 MSM using PrEP, 271 (60.6 %) had HBsAb levels ≥10 mIU/mL, while 176 (39.4 %) <10 mIU/mL at the start of PrEP. Seroprotection was more prevalent among older participants (p = 0.014) and those with higher AST levels (p = 0.019). Of the 55/176 participants who received a booster, 38 (69.1 %) developed protective HBsAb levels. Pre-booster HBsAb levels between 2 and 9.9 mIU/mL were associated with a better booster response (p = 0.032).

CONCLUSIONS

Almost 40 % of MSM using PrEP lacked protective HBsAb three decades after primary HBV vaccination, and around one-third of booster recipients failed to respond. Due to the high-risk nature of this group, systematic HBsAb screening and booster administration are recommended to ensure adequate protection.