Human papillomavirus prevalence and risk factors among Australian women 9-12 years after vaccine program introduction.

BACKGROUND: In Australia, high and widespread uptake of the quadrivalent human papillomavirus (HPV) vaccine has led to substantial population-level reductions in the prevalence of quadrivalent vaccine targeted HPV genotypes 6/11/16/18 in women aged ≤ 35 years. We assessed risk factors for HPV detection among 18-35 year old women, 9-12 years after vaccine program introduction. METHODS: Women attending health services between 2015 and 2018 provided a self-collected vaginal specimen for HPV genotyping (Roche Linear Array) and completed a questionnaire. HPV vaccination status was validated against the National Register. Adjusted odds ratios (aORs) and 95% confidence intervals (CI) were calculated for factors associated with HPV detection. RESULTS: Among 1564 women (median age 24 years; IQR 21-27 years), Register-confirmed ≥ 1-dose vaccine coverage was highest at 69.3% and 68.1% among women aged 18-21 and 22-24 years respectively, decreasing to 42.9% among those aged 30-35 years. Overall prevalence of quadrivalent vaccine-targeted HPV types was very low (2.0%; 95% CI: 1.4-2.8%) and influenced only by vaccination status (5.5% among unvaccinated compared with 0.7% among vaccinated women; aOR = 0.13 (95% CI: 0.05-0.30)). Prevalence of remaining HPV types, at 40.4% (95% CI: 38.0-42.9%), was influenced by established risk factors for HPV infection; younger age-group (p-trend < 0.001), more recent (p < 0.001) and lifetime sexual partners (p-trend < 0.001), but not vaccination status. Prevalence of HPV31/33/45, which shared risk factors with that of non-vaccine targeted HPV types, was also lower among vaccinated (4%) compared with unvaccinated (7%) women (aOR = 0.51; 95% CI: 0.29-0.89), indicative of cross-protection. CONCLUSION: Vaccination has changed the epidemiology of HPV infection in Australian women, having markedly reduced the prevalence of vaccine-targeted types, including amongst women with known risk factors for infection. Vaccinated women appear to be benefiting from modest cross-protection against types 31/33/45 afforded by the quadrivalent HPV vaccine. These results reinforce the importance of HPV vaccination.