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

Abstract

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.

Keywords: HBV; HbsAb; Hepatitis B; Protection; Vaccination.