The Food and Drug Administration (FDA) last week approved a vaccine that protects against the two types of human papillomavirus (HPV) that are responsible for 70 percent of all cases of cervical cancer. The approval covers the vaccine's use in females from ages 9 to 26.

The FDA action comes on the heels of a unanimous vote by the agency's Vaccines and Related Biological Products Advisory Committee that the vaccine, called Gardasil, is both safe and effective in the populations in which it was tested.

Manufactured by Merck & Co., Gardasil is a "quadrivalent" vaccine, meaning that it protects against four HPV types: 6, 11, 16, and 18. While the latter two types are responsible for the large majority of cervical cancer cases, types 6 and 11 are responsible for 90 percent of genital warts cases.

The approval for Gardasil, which is administered as a series of three injections over a 6-month period, includes its use for the prevention of cervical cancer and certain cervical, vulvular, and vaginal precancers called intraepithelial neoplasias.

In large international clinical trials testing Gardasil, it prevented nearly 100 percent of the precancerous cervical cell changes caused by the HPV types targeted by the vaccine for up to 4 years after vaccination.

These efficacy studies included females aged 15 to 26. Because of logistical and ethical concerns, Merck conducted trials in girls aged 9 to 15 only to measure their immune response to the vaccine. Participants in those studies had an even stronger immune response than the older participants in the efficacy trials, which the advisory committee and FDA agreed supported "bridging" or extending the effectiveness data to include this younger group.

Merck is conducting several post-market studies, including those to further evaluate general safety and long-term effectiveness, and to monitor the pregnancy outcomes of women who received Gardasil but didn't know they were pregnant at the time. Merck is also conducting trials to evaluate the safety and effectiveness of Gardasil in males.