Women for the first time have a vaccine to protect themselves against cervical cancer.

The Food and Drug Administration on Thursday approved use of the vaccine, Gardasil, for use in girls and women ages 9 to 26. It works by preventing infection by four strains of the human papillomavirus, or HPV, the most prevalent sexually transmitted disease.

This cancer kills 3,700 women each year in the United States and hundreds of thousands more worldwide. Acting FDA Administrator Dr. Andrew von Eschenbach said the vaccine will have "a dramatic effect" on the health of women around the world.

Related Story: 12 Things You Should Know About the Cervical Cancer Vaccine

Gardasil, manufactured by Merck & Co. Inc., protects against the two types of HPV responsible for about 70 percent of cervical cancer cases. The vaccine also blocks infection by two other strains responsible for 90 percent of genital wart cases. It will be available by the end of June.

Clinical trials showed Gardasil prevented 100 percent of cervical cancer related to the two HPV strains in women who had not been previously infected, Merck said. It also prevented 99 percent of the cases of genital warts caused by the two other strains.

"Fortunately, we can now include the worst types of HPV and most cervical cancer in the list of diseases that no one need suffer or die from ever again," said Alex Azar, deputy Health and Human Services secretary.

The FDA also said the vaccine appeared very safe. However, it's not known how long its protection will last or if women will have to receive booster shots later in life. Merck has agreed to monitor its long-term effectiveness.

Merck is expected to market Gardasil as a cancer vaccine, rather than an STD vaccine. It remains unclear how widespread the use of the three-shot series will be, in part because of its $360 list price. Conservative opposition to making the vaccine mandatory for school attendance may also curb its adoption.

The target age for receiving Gardasil is low because the vaccine works best when given to girls before they begin having sex and run the risk of HPV infection. The vaccine does not protect people already infected and may increase their risk of the kind of lesions that can lead to cervical cancer, the FDA has said. However, a final FDA analysis does not substantiate such a risk, said Dr. Jesse Goodman, director of the agency's Center for Biologics and Evaluation and Research.

The national Advisory Committee on Immunization Practices will decide June 29 whether to endorse routine vaccination with Gardasil. That endorsement is critical if a vaccine is to become a standard of care.

It then will be up to individual states to decide whether to add the vaccine to the list of others required before students may attend public schools.

Conservative groups like Focus on the Family support availability of the vaccine, but oppose making it mandatory, saying the decision to vaccinate should rest with a child's parents or guardians. It promotes abstinence as the best way of warding off infection by HPV and other STDs.

HPV affects more than 50 percent of sexually active adults at some point in their lives. The cervical cancer it can cause kills about 290,000 women worldwide each year, including 3,700 in the United States. In the U.S., regular Pap smears often detect precancerous lesions and early cancer. The vaccine does not eliminate the need for regular screening.

Analysts believe Gardasil sales could top $1 billion a year for Merck, which is battling thousands of lawsuits over its withdrawn painkiller Vioxx. The Whitehouse Station, N.J. company is seeking to license Gardasil in more than 50 countries.

GlaxoSmithKline PLC is also developing an HPV vaccine.

Richard Clark, Merck's chief executive officer and president, called the vaccine a "lifesaving scientific advance."

The cost of Gardasil and the difficulty of getting young girls in to see a doctor three times in six months to receive the vaccine could pose problems, said Cynthia Dailard, senior public policy analyst at the Guttmacher Institute, which focuses on sexual and reproductive health. Ensuring its availability to poor and minority girls and women — and others less likely to receive regular Pap exams — also will be difficult. Merck plans to provide Gardasil for free to the poor and uninsured.

"This is an incredibly exciting breakthrough, but at the same time, it presents some major challenges, some the likes of which we have never confronted before," Dailard said.

Inda Blatch-Geib, an Akron, Ohio mother of four, said she'd consider vaccinating her daughters, ages 9 and 16. Blatch-Geib, 41, said doing so wouldn't be tantamount to giving her girls a green light to have sex.

"Giving the vaccine goes with a conversation. We are pretty open with our children, so it wouldn't be an issue. It would lead to conversations," Blatch-Geib said.

The only other vaccine effective in preventing cancer is against hepatitis B, which can cause liver cancer.