The controversial vaccine for human papillomavirus (HPV) has lowered rates of infection, both in women who were vaccinated and in those who did not receive the vaccine, according to a new study published in the journal Pediatrics.

This phenomenon is dubbed 'herd immunity' - a term that suggests that once a critical number of people has received a vaccination, the larger community can be protected because there's a smaller chance of an outbreak.

In a study of young women ages 13 to 16, researchers at Cincinnati Children's Hospital compared the prevalence of HPV in two groups. In 2006 and 2007, they looked at the rate of HPV infections among 368 girls who had sexual contact but were not vaccinated. In 2009 and 2010, they analyzed the prevalence of HPV among 409 young women, more than half of whom had received at least one dose of the vaccine.
Looking at pre- and post-vaccination HPV rates, they found that the type of HPV prevented by the vaccine had decreased 58 percent overall. As expected, the decrease was highest among vaccinated young women at 69 percent, but they also saw a substantial decrease (49 percent) in the unvaccinated girls.

"Infection with the types of HPV targeted by the vaccine decreased in vaccinated young women by 69 percent," says Jessica Kahn, MD, MPH, a physician in the division of Adolescent Medicine at Cincinnati Children's and lead author of the study. "Two of these HPV types, HPV-16 and HPV-18, cause about 70 percent of cervical cancer. Thus, the results are promising in that they suggest that vaccine introduction could substantially reduce rates of cervical cancer in this community in the future."

Kahn said the decrease among vaccinated young women was "especially remarkable" because many were sexually experienced and exposed to HPV before vaccination, and many only underwent one dose of the vaccine when three are recommended for the most protection, according to CBS News.

The study is "good news that comes surprisingly soon," Dr. William Schaffner, chairman of the department of preventive medicine at Vanderbilt University, told MyHealthNewsDaily. Schaffner said he would have expected a larger portion of the population needed to be vaccinated, including boys, to see herd immunity. The study is a reminder that "vaccination is not just about the individuals getting vaccinated...it's about everyone else in the community," Schaffner said.