A new study published in the Journal of Infectious Diseases found that the prevalence of human papillomavirus (HPV) among teen girls between the ages of 14 and 19 decreased 56 percent — a finding that doctors attribute to the introduction of the HPV vaccine.

According to the Centers for Disease Control and Prevention (CDC), approximately 79 million Americans, most of whom are in their teens and early 20s, are infected with HPV. About 14 million people become infected each year. The HPV vaccine, which was introduced in 2006, is recommended for girls and boys between the ages of 11 and 12. It is given as a series of three shots over a six-month period. The CDC says that the vaccine offers the best results when given to girls and boys before they become sexually active. And, based on the results of this new study, CDC researchers may be on to something.

"Unfortunately only one third of girls aged 13-17 have been fully vaccinated with HPV vaccine. Countries such as Rwanda have vaccinated more than 80 percent of their teen girls," said CDC director Tom Frieden. "Our low vaccination rates represent 50,000 preventable tragedies - 50,000 girls alive today will develop cervical cancer over their lifetime that would have been prevented if we reach 80 percent vaccination rates."

HPV is the most common sexually transmitted infection (STI), infecting the genital areas of males and females as well as the mouth and throat in some cases. The infection can be passed by genital contact, anal sex, or oral sex. While HPV can cause genital warts like other STIs, it is considered especially dangerous because of its link to genital and other serious cancers.

The study compared data from the "vaccine era" (2007-2010) and the "prevaccine era" (2003-2006) to find out whether there was a reduction in the prevalence of HPV types targeted by the vaccine. Researchers, led by CDC's Dr. Lauri Markowitz, M.D., found that the vaccine-type HPV prevalence decreased among teen girls despite low vaccine uptake — meaning the vaccine was very effective.

"The decline in vaccine type prevalence is higher than expected and could be due to factors such as to herd immunity, high effectiveness with less than a complete three-dose series and/or changes in sexual behavior we could not measure," said Markowitz. "This decline is encouraging, given the substantial health and economic burden of HPV-associated disease."

Advocates for HPV vaccination say that the statistics prove what they've been saying all along: it may seem strange to vaccinate pre-teens for STIs, but it will be worth it. "This report shows that HPV vaccine works well, and the report should be a wake-up call to our nation to protect the next generation by increasing HPV vaccination rates."