HPV vaccine reduces infections by 56 percent, CDC says

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The HPV vaccine may be controversial, but it works, new research shows.

The rate of HPV infection among teenage girls dropped from 11.5 percent in the "pre-vaccine era" to 5.1 percent in the "vaccine era," researchers from the Centers for Disease Control and Prevention reported Wednesday in the Journal of Infectious Diseases. That is a drop of 56 percent, the study notes. The infection rates cover the four types of HPV that are targeted by the vaccines Gardasil and Cervarix.

Human papillomaviruses are the most common cause of sexually transmitted infections. More than half of people who are sexually active become infected with one of the more than 40 types of HPV that are known to spread during vaginal, oral or anal sex, according to the National Cancer Institute.

HPVs are responsible for nearly all cases of cervical cancer, along with most cases of anal cancer, the institute says. The viruses also cause more than half the cancers in the middle part of the throat and about half of vaginal, vulvar and penile cancers. Altogether, HPVs are responsible for about 5 percent of all cancers worldwide, according to the institute.

The CDC estimates that HPV causes 19,000 cancers in women and 8,000 cancers in men each year.

A three-dose HPV vaccine was introduced in 2006 and was recommended for girls ages 11 and 12 by the CDC's Advisory Committee on Immunization Practices. Girls and women between the ages of 13 and 26 were advised to get a catch-up version of the vaccine. As of 2011, the panel also recommended the vaccine for boys.

But many parents have been wary of the vaccines in part because of concerns that they could encourage kids to become sexually active. The CDC researchers noted that as of 2010, 49 percent of girls between the ages of 13 and 17 had received at least one dose of the vaccine and 32 percent completed all three doses.

The statistics used in the new study are based on data from the CDC's National Health and Nutrition Examination Survey and include a representative sample of Americans. The surveys from 2003 to 2006 were used for the pre-vaccine era, and surveys from 2007 to 2010 measured the vaccine era. Altogether, a total of 8,403 teens were tested for the four types of human papillomavirus - HPV-6, HPV-11, HPV-16 and HPV-18 - that are targeted by the vaccines.

The 56 percent drop in HPV infection was found for females ages 14 to 19. And there were other indications that immunization worked: Among the teens who got the shots, only 3.1 percent had one of the HPV strains targeted by the vaccines, compared with 12.6 percent of the teens who didn't get the shots. Also, there was no change in infection rates for HPV types that were not targeted by the vaccines.

There was no sign that getting the shots made the teens more promiscuous: 53.9 percent said they were sexually active in the pre-vaccine years, and 50.3 percent were having sex after the vaccine became available.

"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," Dr. Tom Frieden, director of the CDC, said in a statement.

"Unfortunately only one-third of girls aged 13 to 17 have been fully vaccinated with HPV vaccine," he said. If the vaccination rate were 80 percent, 50,000 cases of cervical cancer among girls alive today could be prevented, he said.