Winer RL, Lin J, Querec TD, et al. - In the United States, recommendation of HPV vaccination for males aged 11–12 years has been made since 2011, with catch-up vaccination through age 26 years for previously unvaccinated men who have sex with men (MSM). HPV prevalence among vaccinated MSM was investigated and compared with that among MSM with no/unknown vaccination history. Overall, 348 of 687 participants (50.7%) self-reported ever receiving ≥ 1 HPV vaccine dose. Significantly lower prevalence was observed in participants vaccinated at age ≤ 18 years vs those with no/unknown vaccination, corresponding to a vaccine effectiveness of 85% against 4vHPV-type HPV. HPV vaccination is thus suggested as effective in preventing penile HPV infections in young MSM when it is administered at age ≤ 18 years.