Benefits of Early HPV Vaccination Emerge Rapidly
The benefits of vaccinating adolescent girls against human papillomavirus (HPV) are already evident by the midteenage years, according to an analysis of data from a Canadian program that offers free school-based vaccination to eighth-grade girls.
"This study provides new, strong evidence of the impact of [quadrivalent HPV] vaccination on reductions in cervical dysplasia among adolescent girls. Although imprecise, we also observed apparent reductions in [anogenital warts]," Leah M. Smith, MSc, from the Departments of Epidemiology, Biostatistics, and Occupational Health, McGill University, Montreal, Quebec, Canada, and colleagues write.
"The fact that these benefits were observed in such a young age group strengthens current recommendations that vaccination should occur at an early age," they maintain.
The researchers report their findings in an article published online April 27 and in the May issue of Pediatrics.
For the retrospective population-based cohort study, the investigators used administrative health databases of Ontario, Canada, to identify girls in eighth grade in the 2 years before and in the 2 years after 2007, when the province implemented the program. Girls could be vaccinated in school-based immunization clinics or by a physician or at their health unit.
In all, the investigators compared HPV-related outcomes between 131,781 girls who were ineligible and 128,712 girls who were eligible for the vaccination program. On average, the girls were 13.2 years old at baseline and had follow-up for 4.6 years. Slightly more than half of the eligible girls were actually vaccinated against HPV, receiving all three doses in the series within a year.
Results showed that 0.94% (n = 2436) of the study cohort overall received a diagnosis of cervical dysplasia during follow-up. Girls had a significant 21% (95% confidence interval [CI], 6% to 34%) lower risk for dysplasia if they were eligible for the vaccination program, amounting to 2.32 (95% CI, −4.02 to −0.61) fewer cases per 1000 girls. In addition, they had a 44% (95% CI, 13% - 64%) lower risk if they were actually vaccinated, amounting to 5.70 (95% CI, −9.91 to −1.50) fewer cases per 1000 girls.
Stated another way, one case of cervical dysplasia was prevented for every 431 (95% CI, 248 - 1639) girls eligible for the vaccination program and for every 175 (95% CI, 101 - 667) girls actually vaccinated.
Overall, 0.15% (n = 400) of the cohort received a diagnosis of anogenital warts during follow-up. There were nonsignificant trends whereby girls had a 19% lower risk for anogenital warts if they were eligible for the program (0.34 fewer cases per 1000 girls; 95% CI, −1.03 to 0.36) and a 43% lower risk if they were vaccinated (0.83 fewer cases per 1000 girls; 95% CI, 0.20 - 1.58).
"[P]olicy makers and physicians can use these findings to substantiate arguments that delaying vaccination may result in missed opportunities for prevention," the investigators conclude. "In addition, cost-effectiveness studies should be updated to incorporate real-world estimates of program- and vaccine-level effectiveness and coverage to provide more accurate assessments of the value of [quadrivalent HPV] vaccination," they recommend.
The authors have disclosed no relevant financial relationships.
Pediatrics. Published online April 27, 2015. Abstract