The cervical cancer vaccine Gardasil also works to prevent cancers of the vagina and vulva, federal health officials said Friday, as they approved expanding its use to protect against those diseases as well.

The Food and Drug Administration first approved Gardasil in 2006 for the prevention of cervical cancer in girls and women ages 9 to 26. The vaccine works by protecting against strains of the human papillomavirus, or HPV, that cause about 70 percent of cervical cancers. The HPV virus, transmitted by sexual contact, causes genital warts that sometimes develop into cancer.

"There is now strong evidence showing that this vaccine can help prevent vulvar and vaginal cancers due to the same virus for which it also helps protect against cervical cancer," said Dr. Jesse Goodman, director of the FDA center that oversees vaccines.

Some 15,000 women were followed for about two years as part of a clinical study. One group had been vaccinated with Gardasil, while the other had not. In the group that did not get the vaccine, 10 women developed precancerous vulvar lesions, and nine developed similar vaginal lesions because of HPV infection. No women in the Gardasil group developed such lesions.

The government estimates that there are 3,460 new cases of vulvar cancer and 2,210 new cases of vaginal cancer each year. Cervical cancer is more common, with an estimated 11,070 new cases each year and nearly 3,900 deaths.

Gardasil is manufactured by Merck & Co., Inc. The vaccine, given in three doses over a six-month period, costs about $375.