Reduced prevalence of vulvar HPV16/18 infection among women who received the HPV16/18 bivalent vaccine: A nested analysis within the Costa Rica Vaccine Trial

Background: Vaccine efficacy (VE) against vulvar human papillomavirus (HPV) infection has not been reported and data regarding its epidemiology are sparse. Methods: Women (n = 5404) age 22-29 present at the 4-year study visit of the Costa Rica Vaccine Trial provided vulvar and cervical samples. A subset (n = 1044) was tested for HPV DNA (SPF₁₀/LiPA₂₅ version 1). VE against 1-time detection of vulvar HPV16/18 among HPV vaccinated versus unvaccinated women was calculated and compared to the cervix. Prevalence of and risk factors for HPV were evaluated in the control arm (n = 536). Results: Vulvar HPV16/18 VE (54.1%; 95% confidence interval [CI], 4.9%-79.1%) was comparable to cervix (45.8%; 95% CI, 6.4%-69.4%). Vulvar and cervical HPV16 prevalence within the control arm was 3.0% and 4.7%, respectively. Independent risk factors for vulvar HPV were similar to cervix and included: age (adjusted odds ratio [aOR] 0.5 [95% CI,.3-.9] ≥28 vs 22-23]); marital status (aOR 2.3 [95% CI, 1.5-3.5] single vs married/living-asmarried); and number of sexual partners (aOR 3.6 [95% CI, 1.9-7.0] ≥6 vs 1). Conclusions: In this intention-to-treat analysis, VE against vulvar and cervical HPV16/18 were comparable 4 years following vaccination. Risk factors for HPV were similar by anatomic site. Clinical Trials Registration: NCT00128661.