Impacts of Human Papillomavirus Immunization Programs on Rates of Anogenital Warts in British Columbia, Canada, 2000 to 2017.

Background: In 2008, British Columbia (BC) implemented a school-based quadrivalent human papillomavirus (HPV-4) immunization program for girls born in 1994 or later. In 2015, an expanded clinic-based program included men who report sex with men (MSM) born in 1989 or later. To evaluate the impacts of HPV-4 programs on anogenital warts (AGWs), diagnosis rates were measured among women who report sex with men (WSM), men who report sex with women (MSW), and MSM.

Methods: Diagnoses of AGW were ascertained from 16 sexually transmitted infection clinics. Rates were calculated as new AGW diagnoses over person-years (py) at risk and stratified by age group, calendar period, and birth cohort. Adjusted relative rates (aRR) were estimated using multivariable Poisson regression.

Results: There were 204,832 clinic visits by 85,158 individuals: 28,366 (33%) WSM, 35,688 (42%) MSW, and 14,534 (17%) MSM. After adjusting for age and period, AGW rates in the 1994-1996 birth cohort decreased by 56% overall (1.21 vs. 2.72 cases/100 py; aRR, 0.44; 95% confidence interval [CI], 0.34-0.59), 65% among WSM (0.97 vs. 2.77 cases/100 py; aRR, 0.35; 95% CI, 0.22-0.57), 58% among MSW (1.60 vs. 3.78 cases/100 py; aRR, 0.42; 95% CI, 0.28-0.65), and 41% among MSM (1.14 vs. 1.19 cases/100 py; aRR, 0.59; 95% CI, 0.38-0.91) versus the 1991-1993 birth cohort.

Conclusions: The HPV-4 programs had significant impacts on lowering AGW rates in BC. The greatest decrease was among WSM eligible for the school-based program, followed by birth cohorts of men who likely have sex with HPV-4 eligible women. The smallest decrease among MSM may reflect the later introduction of the clinic-based program.