Impact of Counselling on the Uptake of STI-Preventive Vaccines Among MSM Using PrEP: A Retrospective Cohort Study in Policlinico Umberto 1, Italy

INTRODUCTION: The introduction of pre-exposure prophylaxis (PrEP) has significantly improved HIV prevention among men who have sex with men (MSM). Vaccination against hepatitis A (HAV), hepatitis B (HBV), human papillomavirus (HPV), and monkeypox (Mpox) is strongly advised for MSM, yet coverage remains suboptimal. Recent studies suggest moderate effectiveness against gonorrhoea infection from the 4-component MenB vaccine (4CMenB). This study evaluates the impact of targeted counselling strategies on the uptake of STI-preventive vaccines in a cohort of MSM on PrEP at Policlinico Umberto I, Rome. METHODS: This retrospective observational cohort study analysed 511 MSM receiving PrEP between January 2021 and December 2024. Participants were assessed for baseline vaccination status and uptake over an 18-month period. The primary outcome was vaccination coverage at follow- up, while the secondary outcome was STI incidence. Statistical analyses included chi-square tests and t-tests to compare vaccination rates across time points and age groups. RESULTS: At baseline, vaccination coverage was low for HAV (9.8%), HPV (17.6%), 4CMenB (5.9%), HBV (52.6%), and Mpox (48.9%). After 18 months, significant increases were observed (HAV: 56.4%, HPV: 63.6%, 4CMenB: 20.3%, HBV: 86.1%, and Mpox: 65.6%, p