Far fewer teen girls and young women have been infected with the cancer-causing human papillomavirus (HPV) since a vaccine that protects against the virus was first introduced a decade ago.

Infection rates among teens ages 14 to 19 dropped by 64 percent six years after health providers first began recommending the shot to girls and young women, according to new research published in the journal, Pediatrics. For women 20 and 24, the decline was 34 percent.









The steep drop was somewhat surprising, researchers noted, given the low vaccination rates for HPV. Just 38 percent of girls had received all three doses of the vaccine, the study found. Meanwhile, 57 percent had received at least one dose.

Researchers suggested several possible reasons for the sharp decline in HPV infections despite low vaccination rates. Among them: perhaps a lesser dose of the vaccine provided enough protection, or maybe something called “herd immunity” was at work. Having enough people vaccinated controls the spread of the virus, protecting even those who have not been inoculated.

HPV spreads through sexual intercourse and infects the skin, genital area, mouth and throat. It is also a primary cause of cervical cancer.

Though health officials endorse it as an effective cancer prevention tool, some parents are reluctant to have their children vaccinated for HPV — fearing that it amounts to granting their children tacit approval to become sexually active. Other parents worry about the vaccine’s potential side effects. And Michele Bachmann made her objections to the vaccine an issue during her 2012 presidential campaign.

Doctors recommend the vaccine for both boys and girls, starting at age 11 or 12. The shot can be administered to women up to 26 and men up 21.

The Pediatrics study examined the infection rates for girls only because doctors did not start recommending vaccination for boys until 2011.


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