Merck's Gardasil Cleared by FDA

The FDA approved the vaccine based on four clinical trials involving 21,000 women ages 16 to 26 who were given Gardasil or a placebo. "The results showed that in women who had not already been infected, Gardasil was nearly 100% effective" in preventing certain precancerous lesions and genital warts caused by the HPV types targeted by the vaccine, the FDA says.

"While the study period was not long enough for cervical cancer to develop, the prevention of these cervical precancerous lesions is believed highly likely to result in the prevention of those cancers," the FDA says.

The FDA decided to approve the vaccine for younger girls based on two studies that measured their immune systems' response, showing that this response "was as good as that found in 16-26 year olds, indicating that the vaccine should have similar effectiveness when used in the 9- to 15-year age group."