According to a July 9 study(pediatrics.aappublications.org) (abstract) in Pediatrics, data suggest that the quadrivalent human papillomavirus (HPV4) vaccine is responsible for a marked downturn in the number of cases of HPV infection caused by strains contained in the vaccine reported among those immunized against the virus, as well as a decrease in cases among those who are not so protected.
"Clinical trials have demonstrated that prophylactic HPV vaccines are highly effective in preventing HPV infection, but the impact of vaccination on HPV prevalence rates in real-world, community settings is uncertain," the researchers wrote. "This study provides evidence of a substantial decrease in the prevalence of vaccine-type HPV among young women and evidence of herd protection in a community only four years after the (HPV4) vaccine was licensed."
The study recruited 368 sexually active, unvaccinated young women ages 13-16 in 2006 and 2007 before later recruiting a group of 409 participants in the same age range, of which more than half had received at least one dose of the vaccine. Comparing the two groups, researchers found that cases of vaccine-type HPV infection were reduced by
- A recent study in Pediatrics suggests that the quadrivalent human papillomavirus (HPV) vaccine is responsible for a marked downturn in the number of reported cases of HPV infection caused by strains contained in the vaccine among those immunized against the virus.
- The study also reports a decrease in cases among individuals who have not been so immunized, which is thought to be due to so-called herd protection
- An increase in HPV infections caused by strains not contained in the vaccine among vaccinated participants may be due to type replacement and warrants further study.
- 58 percent overall,
- 69 percent among vaccinated participants and
- 49 percent among unvaccinated participants.
"This change is especially remarkable given that participants were sexually experienced, a substantial proportion was exposed to vaccine-type HPV before vaccination, and only one HPV vaccine dose was required to be considered 'vaccinated' in this analysis," the researchers wrote.
"As the high-risk vaccine-type HPV (strain)s HPV-16 and -18 are responsible for most cases of moderate/severe cervical intraepithelial neoplasia (CIN) in young women and cause 70 percent of invasive cervical cancer (ICC) cases, the results are promising in terms of their implications for declining rates of CIN and, ultimately, ICC in this community in the future."
HPV4 was licensed by the FDA for use in females in June 2006, with the bivalent HPV (HPV2) vaccine getting FDA clearance for this population in October 2009. The CDC's Advisory Committee on Immunization Practices recommended(www.cdc.gov) routine vaccination of girls and women ages 9-26 with HPV4 in March 2007 and expanded its recommendation in late October 2011 to include routine HPV4 vaccination of boys and young men.
Not all of the study's findings were positive, however, because researchers also reported an increase in nonvaccine-type HPV in vaccinated participants, which they said warrants further study.
"The prevalence of nonvaccine-type HPV and high-risk nonvaccine-type HPV increased significantly among all women and among vaccinated women, but not among unvaccinated women, a finding that could be consistent with type replacement," the researchers wrote. "A possible explanation … is that their risk for HPV may differ. Vaccinated versus unvaccinated girls did not differ in number of recent and lifetime sexual partners; however, they were more likely to be African American and reported, on average, an earlier age of first sexual intercourse, both of which have been associated with higher rates of HPV infection.
"Only serial surveillance studies in this population, as well as regional or national surveillance studies with larger study samples over longer periods of time, will definitively address the issue of type replacement after vaccination."