Population-level Impact of HPV Vaccination on the Incidence of Genital Warts in Sweden

Abstract

Background Sweden introduced HPV vaccination in 2006, administered through opportunistic, subsidized, catch-up and school-based programs. Notably, genital warts (GW) are the first observable clinical outcome following infection by HPV-6/11, targeted by vaccination. We aim to gain knowledge of the incidence of GW in Sweden and evaluate its change throughout vaccination programs. Methods This ecological study used Swedish registers to obtain national population data and cases of genital warts from 2006-2018 in men and women aged 15-44. We used Poisson models to evaluate GW incidence change after vaccination in reference to a pre-vaccination period, stratified by age and sex. As well as, to estimate incidence change of GW in birth cohorts eligible for vaccination compared to a pre-vaccination cohort. Finally, we estimated GW cases averted in each vaccinated cohort. Results The incidence of GW decreased during periods following HPV vaccination. In 2016-2018, over a decade after vaccination availability, incidence decreased by 89% (95% CI 83-93), 73% (95% CI 71-75), 50% (95% CI 43-56) and 20% (95% CI 10-28) in women aged 15-19, 20-24, 25-29 and 30-34, respectively. A similar reduction was observable in men, although of lesser magnitude. We estimated 18,890 and 12,343 GW cases averted among vaccinated cohorts of women and men, respectively. Conclusions We report on population-level decreases of GW incidence in women and men following increased vaccination coverage. Cohorts eligible for school-based vaccination recorded the largest decrease in GW incidence in Sweden to date. For the period under study, decreases among men could be attributed to herd effects.