BACKGROUND: The province of Quebec (Canada) has had a school-based Human Papillomavirus (HPV) vaccination program with high coverage since 2008, with more than 90% of girls having received at least one quadrivalent vaccine (4vHPV) dose by age 15. In 2018, Quebec was the first jurisdiction to switch to a mixed schedule (nonavalent+bivalent), and as such wanted to evaluate it. However, when devising an evaluation strategy for new vaccine schedules, the presence of herd effect needs to be ascertained. With this in mind, this study aimed to measure HPV prevalence among unvaccinated 16-20-year-old sexually active men. METHODS: In 2020-2022, men were recruited from schools and online across the province of Quebec. Participants completed an online questionnaire and provided a self-collected penile swab (surface) for HPV detection and genotyping (Anyplex™ II-HPV28 Detection assay). Risk factors associated with HPV positivity were assessed. Vaccination status (unvaccinated) was verified through the Quebec Vaccination Registry. RESULTS: Overall, 369 participants provided a sample suitable for HPV testing. HPV prevalence was 18.4% (95%CI:14.6-22.8). Only two participants harbored a 4vHPV-targeted genotype (0.5%
95%CI:0.1-1.9), both reporting sexual contact with men. In multivariate analysis, age, greater number of lifetime sexual partners and history of other sexually transmitted infections were independently associated with positivity for at least one HPV genotype. CONCLUSION: The low 4vHPV-targeted genotypes prevalence (˂1%) among unvaccinated men of the same age as women vaccinated with 4vHPV suggests a strong herd immunity among young adults in Quebec. Evaluation of schedule changes will have to take this finding into account.