According to a Swedish study initial vaccinations for human papillomavirus (HPV) at a young age is important for maximizing quadrivalent HPV vaccine effectiveness. The study was published on March 13 in the Journal of the National Cancer Institute.
HPV vaccination programs have been launched around the world in hopes of preventing cervical cancer and other HPV-related cancers. While incidence of genital warts is the earliest possible disease outcome to measure the efficacy of the HPV vaccine, the results of such efficacy trials may not be fully generalizable to real-life HPV vaccination programs. Furthermore, incidence of genital warts after on-demand vaccination with quadrivalent HPV vaccine using individual-level data remains unknown.
In order to determine the efficacy of maximizing HPV vaccines at a young age, Amy Leval, R.N., of the Department of Medical Epidemiology and Biostatistics at Karolinska Institutet in Stockholm, Sweden and colleagues, looked at a cohort of females ages 10 to 44 years living in Sweden between 2006-2010 who were linked to multiple population registers to identify genital warts incidence in relation to HPV vaccination. Incidence rate ratios of genital warts were estimated using time-to-event analyses with adjustment for attained age and parental education level, stratified by age at first vaccination.
In an accompanying editorial, Jennifer S. Smith, Ph.D., M.P.H., of the Gillings School of Global Public Health, University of North Carolina, and Elisabete Weiderpass, Ph.D., of Karolinska Institutet, write that the low HPV vaccination coverage before the national school-based program in Sweden was implemented gave the opportunity to compare the incidence of genital warts in vaccinated cohorts with that in unvaccinated cohorts. "Future studies in Sweden—and elsewhere where HPV vaccine coverage rates are high in target populations, such as Australia and Canada—may need to compare vaccinated birth cohorts with older birth cohorts that were previously unvaccinated to evaluate the impact of vaccination on the population level."