Early impact of Ontario’s human papillomavirus (HPV) vaccination program on anogenital warts (AGWs): a population-based assessment

Introduction — This study aimed to evaluate the early population impact of Ontario's school-based human papillomavirus (HPV) vaccination program, implemented in September 2007 for grade 8 females, by comparing anogenital wart (AGW) healthcare utilization before and after vaccine program implementation, in program-eligible and program-ineligible cohorts, focusing on 15-26year olds.

Methods — Using a retrospective longitudinal population-based study design, health administrative data were used to identify incident AGWs and total health service utilization (HSU) for AGWs for Ontario residents 15 years and older between April 1 2004 and March 31 2014. The study period was divided into two eras: the pre-vaccine program era and the vaccine program era. Negative binomial models were generated to analyze trends across time by age group and sex. We adjusted female rates for routine Papanicolaou (Pap) testing to address spillover effects of Pap smear policy changes on AGW diagnosis.

Results — Between fiscal years 2004 and 2013, AGW incidence decreased 2.6% on average per year in 15-17 year old females, and total HSU for AGWs decreased an average of 4.8% and 2.2% per year in 15-17 and 18-20 year old females. Comparing the vaccine era to the pre-vaccine era, AGW incidence decreased 6.5% in 18-20 year old females, and AGW HSU decreased 13.8%, 11.1%, and 10.0% in 15-17, 18-20, and 21-23 year old females respectively. In contrast, male AGW incidence rates increased an average of 4.1%, 2.8%, and 0.9% per year in 15-17, 21-23, and 24-26 year old males respectively. AGW incidence rates increased 12.2% in 15-17 year old males from the pre-vaccine to vaccine era.

Conclusion — The decline in AGW incidence and HSU in program-eligible females suggests the school-based HPV vaccination program has had an early population impact in Ontario. The increasing AGW incidence in males suggests no early evidence of herd effects in males.