The FDA approval stemmed from a two-year follow-up analysis by Gardasil's manufacturer, Merck, of the more than 15,000 girls and women given Gardasil or placebo in the original studies aimed at testing the vaccine's effectiveness in preventing cervical cancer.
Gardasil was "highly effective" in preventing HPV-related precancerous vulvar and vaginal lesions among those who tested negative for HPV types 16 and 18, according to the FDA.
HPV 16 and 18 cause 70% of all cervical cancers and some vulvar and vaginal cancers, although the latter percentages are unknown, according to the FDA.
Among those in the control group of the trial, 10 women developed precancerous vulvar lesions and nine developed precancerous vaginal lesions. All lesions were related to HPV types 16 or 18.
For women who were previously infected, the vaccine showed no benefit.
In addition to expanding the use of Gardasil to protect against vulvar and vaginal precancerous lesions, Merck revised the label to say that information is insufficient to support use past the age of the current FDA-approved age of 26.
Also, Merck added new information to indicate that Gardasil does not protect against diseases caused by HPV types not contained in the vaccine.
In 2006, the FDA approved Gardasil for the prevention of cervical cancer and precancerous genital lesions caused by HPV types 6, 11, 16, and 18 and genital warts caused by HPV types 6 and 11, in a routine three-dose injection of girls ages 11 and 12.