Induced abortion rates among women vaccinated against human papillomavirus: Registry-based follow-up of a community-randomized trial

Abstract

OBJECTIVE: Concerns have been raised that human papillomavirus (HPV)-vaccination programs may alter risk perceptions and increase risk-taking sexual behavior among adolescents. This study aimed to assess induced abortion rates (as a potential indicator of such behavior) between vaccinated and unvaccinated individuals. METHODS: This longitudinal, cluster-randomized cohort study included 6200 HPV-vaccinated women born in 1992-1993 who participated in a 2007 launched HPV-vaccination trial in Finland, and 19,473 unvaccinated women born in 1990-1991 from the same communities. Registry data from a 12-year follow-up period (between 2007 and 2020, depending on the group) up to the age of 28 years was obtained from The Finnish Register on Induced Abortions. RESULTS: Incidence rate of induced abortions per 10,000 person-years was significantly lower among HPV-vaccinated (145.6(95 %CI 137.1,154.5)) compared to unvaccinated individuals (161.4(95 %CI 156.4,166.7)). HPV-vaccinated individuals induced abortions in earlier gestational weeks (p = 0.049). Up to four-years post sexual health education given at HPV vaccination visits, induced abortion rates were significantly lower among individuals aged 15-19 (33.7(95 %CI 29.8,38.2)) than age-aligned unvaccinated controls (42.4(95 %CI 38.9,44.1)). CONCLUSIONS: HPV-vaccinated had lower induced abortion rates than unvaccinated individuals. When further developing HPV-vaccination programs, simultaneous sexual health education should be considered to comprehensively improve the reproductive health of adolescents.