Understanding type replacement following HPV vaccination is important.

We studied the occurrence of specific HPV types in a large cohort of young women from Finland who participated in a population-based HPV vaccination trial. A total of 4,808 16- to 17-year-old women were enrolled in the randomised PATRICIA efficacy trial of HPV16/18 vaccine (Cervarix) compared to hepatitis A virus (HAV) vaccine. HPV infection was assessed from cervical samples obtained every 6 months for 4 years post-vaccination and tested for 14 high- risk HPV types and 2 low-risk HPV types. HPV16/18 vaccination coverage varied from 1% to 22% by participating community. HPV incidence rate ratios (IRRs) in baseline positive women vs. baseline negative women were calculated. In the control arm, baseline HPV18-positive women showed an increased risk of acquiring other clade A7 HPV types (39/45/59/68) (IRR 1.8, 95% confidence interval = 1.01–3.1). No excess risk of non-vaccine HPV types was observed in the baseline HPV DNA-negative HPV16/18-vaccinated women compared to the baseline HPV DNA-negative control women. Similarly, no excess risk was observed in the baseline HPV-16/18-positive HPV16/18-vaccinated women compared to the baseline HPV16/18-negative women. In conclusion, we found no increased rates of non-vaccine HPV types suggestive of type-replacement up to 4 years post-vaccination among HPV16/18-vaccinated young women. However, surveillance of clinical trial cohorts and other populations in countries with HPV vaccination programmes implemented with focus on vaccination coverage rates are warranted.