Monitoring vaccine effectiveness (VE) in large-scale vaccination programs is of great importance for assessing the population impact of immunization. This study aimed to estimate the VE of the bivalent HPV vaccine against 12-month type-specific persistent infection up to six years post-vaccination among young Dutch women.
In 2009, girls 14-16 years of age, who were eligible for the HPV catch-up vaccination campaign in the Netherlands, were invited for participation in a cohort study. Both vaccinated and unvaccinated girls were included and baseline measurements were performed before vaccination. Yearly, questionnaire data and vaginal self-swabs were obtained. Vaginal self-swab material was analyzed with the SPF10-LIPA system. Persistence was defined as at least two consecutive measurements testing positive for the same HPV type, preceded by a high-risk (hr) -negative measurement at baseline or two type-specific negative measurements during follow-up. Type specific hazard ratios were obtained through survival analysis by using the Prentice Williams-Peterson total-time approach, adjusting for ethnicity, age, and sexual behavior. We calculated VE as (1-hazard ratio)*100%.
In total 1593 women (46% vaccinated, 54% unvaccinated) had an available baseline sample, were unvaccinated or vaccinated completely in accordance to the Dutch schedule (at that time 3 doses at 0, 1 and 6 months) and negative for high-risk (hr) HPV at baseline. High VE was observed against vaccine types HPV16 and HPV18 of 95% (95%CI 66%-99%) and 100% (hazard rates per 100 person years: unvaccinated 2.07 (95% CI 1.12-3.86) and vaccinated 0.00 (95%CI 0.00-0.14)), respectively. We observed significant cross-protection against HPV31 (73%, 95%CI 3%-92%). We estimated a VE of 16% (95%CI -14-38%) against all hrHPV-types combined, and a VE of 51% (95%CI 24-69%) against hrHPV-types included in the nonavalent HPV vaccine (HPV16/18/31/33/45/52/58).
The bivalent vaccine shows high effectiveness against 12-month persistent infections by HPV16 and HPV18 among young Dutch women, vaccinated at age 14-16 years while hrHPV negative at baseline, up to six years post-vaccination. Additionally, we found significant cross-protection against 12-month persistent infections by HPV31.