Long-Term Follow-Up Of Human Papillomavirus Type Replacement Among Young Pregnant Finnish Females Before And After A Community-Randomisedhpvvaccination Trial With Moderate Coverage

Large scale human papillomavirus (HPV) vaccination against the most oncogenic high-risk human papillomavirus (HPV) types 16/18 is rapidly reducing their incidence. However, attempts at assessing if this leads to an increase of nonvaccine targeted HPV types have been hampered by several limitations, such as the inability to differentiate secular trends.We performed a population-based serological survey of unvaccinated young women over 12 years. The women were under 23-years-old, residents from 33 communities which participated in a community-randomised trial (CRT) with approximately 50% vaccination coverage. Serum samples were retrieved pre-CRT and post-CRT implementation. Seropositivity to 17 HPV types was assessed. HPV seroprevalence ratios (PR) comparing the postvaccination to prevaccination era were estimated by trial arm. This was also assessed among the sexual risk-taking core group, where type replacement may occur more rapidly. In total, 8022 serum samples from the population-based Finnish Maternity Cohort were retrieved. HPV types 16/18 showed decreased seroprevalence among the unvaccinated in communities only after gender-neutral vaccination (PR16/18A= 0.8, 95% CI 0.7-0.9). HPV6/11 and HPV73 were decreased after gender-neutral vaccination (PR6/11A= 0.8, 95% CI 0.7-0.9, PR73A= 0.7, 95% CI 0.6-0.9, respectively) and girls-only vaccination (PR6/11B= 0.8, 95% CI 0.7-0.9, PR73B= 0.9, 95% CI 0.8-1.0). HPV68 alone was increased but only after girls-only vaccination (PR68B= 1.3, 95% CI 1.0-1.7, PRcore68B= 2.8, 95% CI 1.2-6.3). A large-scale, long-term follow-up found no type replacement in the communities with the strongest reduction of vaccine HPV types. Limited evidence for an increase in HPV68 was restricted to girls-only vaccinated communities and may have been due to secular trends ( number: NCT00534638).