HPV Vaccine Effectiveness by Age and Timing of Vaccination Relative to Age at First Sex Among Men Who Have Sex with Men – Seattle, Washington, 2018-2020

Men who have sex with men (MSM) are at high risk for anal human papillomavirus (HPV) infection, the primary cause of anal cancer. HPV vaccines are approved for individuals aged 9-45 years. We evaluated the effectiveness of the vaccine at preventing vaccine-type anal HPV infection among 18–45-year-old MSM using surveillance data from a sexual health clinic in Seattle, Washington from 2018-2020. Residual specimens from rectal swabs that were self-collected for routine chlamydia and gonorrhea testing were sent to the Centers for Disease Control and Prevention (CDC) laboratory for polymerase chain reaction-based HPV testing. Specimens were genotyped for 19 high-risk HPV types and 9 low-risk HPV types. For each specimen, demographic, clinical, sexual behavioral, and HPV vaccination data were extracted from routine clinical questionnaires and electronic medical records. We used log-binomial regression to calculate adjusted prevalence ratios (aPRs) and 95% confidence intervals (CIs) for associations between ever having received ≥1 dose of HPV vaccine and quadrivalent HPV vaccine-type (4vHPV-type) anal HPV detection, by age group (18-26, 27-35, and 36-45 years). We also evaluated age at vaccination and age at vaccination relative to age at first sex as exposures in separate models among those aged 18-26, and age at vaccination among those aged 27-35. All analyses were adjusted for race and ethnicity, history of pre-exposure prophylaxis (PrEP) use for HIV prevention, and lifetime number of sex partners of any sex. Among 1092 individuals included, documented vaccination history was observed in 290 of the 486 individuals aged 18-26 (59.7%), 130 of the 328 individuals aged 27-35 (39.6%), and 53 of the 278 individuals aged 36-45 (19.1%). Among those aged 18-26, 4vHPV-type HPV prevalence was higher in vaccinated versus unvaccinated individuals (aPR 1.49 [95% CI: 1.06-2.09). However, when considering age at vaccination, we observed a lower prevalence of 4vHPV-type HPV among those who received their first dose at or before age 18 (5.7%) compared with those who were unvaccinated (21.9%), indicating a significant protective association (aPR 0.26 [95% CI: 0.08-0.80]). Similarly, when stratified by timing of vaccination relative to age at first sex, we observed a lower prevalence of 4vHPV-type HPV among those vaccinated prior to first sex (2.9%) compared to those who were unvaccinated (21.9%), indicating a significant protective association (aPR 0.15 [95% CI: 0.02-1.07]). Among those aged 27-35, a history of HPV vaccination was not associated with 4vHPV-type HPV prevalence (aPR 0.75 [95% CI: 0.55, 1.03]). However, when considering age at vaccination, we found that the prevalence was lower among those vaccinated between the ages of 18 and 26 (23.7%) compared to those who were unvaccinated (41.9%), indicating a significant protective association (aPR 0.56 [95% CI: 0.36-0.87]). We did not observe a significant association between vaccination status and 4vHPV-type HPV infection among those aged 36-45 (aPR 1.07 [95% CI: 0.77, 1.50]). Results suggest the vaccine is effective when administered at younger ages and/or before first sex. Results do not suggest significant effectiveness among those vaccinated after age 27.