(HealthDay News) – Following introduction of the human papillomavirus (HPV) vaccine there has been a significant decrease in the prevalence of vaccine-type HPV among vaccinated young women and evidence of herd protection in unvaccinated women, according to a study published online July 9 in Pediatrics.

Jessica A. Kahn, MD, MPH, from the Cincinnati Children’s Hospital Medical Center, and colleagues compared prevalence rates of HPV in young women before and after HPV vaccine introduction. Young women aged 13–26 years who had had sexual contact were recruited for a prevaccination study in 2006–2007 (368 women; 0% vaccinated) and a postvaccination study in 2009–2010 (409 women; 59% vaccinated). Participants were tested for cervicovaginal HPV DNA and completed a questionnaire. Differences in covariates were balanced using propensity score weighting.

After propensity score weighting, the researchers found that, among all participants (mean age, 19 years), the prevalence rate for vaccine-type HPV decreased significantly (31.7% to 13.4%). The decrease occurred among vaccinated (31.8% to 9.9%) and also among the unvaccinated (30.2% to 15.4%) postsurveillance study participants. For vaccinated postsurveillance study participants there was a significant increase in nonvaccine-type HPV (60.7% to 75.9%).

“Four years after licensing of the quadrivalent HPV vaccine there was a substantial decrease in vaccine-type HPV prevalence and evidence of herd protection in this community,” the authors write. “The increase in nonvaccine-type HPV in vaccinated participants should be interpreted with caution but warrants further study.”

Several authors disclosed financial ties to Merck, which manufactures one of the HPV vaccines currently available.

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