While an experimental vaccine to prevent cervical cancer holds great promise, questions remain about who would get the vaccine and how widespread use might be encouraged.

"It's just a horrible disease to have," said Dr. Tauseef Ahmed, head of oncology at Westchester Medical Center in Valhalla. "If you can prevent this disease from occurring, this vaccine is tremendous."

Merck & Co. released results Thursday of a large clinical trial showing that its vaccine, Gardasil, was 100 percent effective in preventing cervical cancer caused by two common types of viruses. The study results on the vaccine were presented yesterday at a meeting of the Infectious Diseases Society of America.

The vaccine must still be approved by the Food and Drug Administration. Merck hopes to begin selling Gardasil late next year.

Cervical cancer is most commonly caused by the human papillomavirus, or HPV, which is a sexually transmitted disease that can also cause genital warts. The vaccine works by preventing infection from two common strains of HPV that are linked to 70 percent of cervical cancers in the United States.

"It's incredibly exciting for all of those women who won't have to worry about cervical cancer," said Sara Goldberger, a cancer survivor and the program director at Gilda's Club of Westchester in White Plains. The club provides support services for cancer patients.

An estimated 10,000 new cases of cervical cancer were diagnosed nationally last year.

Ahmed said in order to truly prevent cervical cancer, both men and women need to be immunized.

About 20 million men and women in the United States are believed to be infected with HPV and men can give it to their partners.

Dr. Ephraim Resnik, a gynecological oncologist in Pomona, said the development of the experimental vaccine was an exciting breakthrough because the human papillomavirus was so common.

But Resnik, who did research on the virus as a student, said the vast majority of women who are infected with HPV do not develop cervical cancer.

"So are we going to give the vaccine to everyone?" he said. "And do we give to females and not males? At what age? And what about people whose cultural beliefs about premarital relations put them at low risk of getting HPV? Is the state going to mandate that they get the vaccine, too?"

The 12,000 or so participants in the Merck study were between the ages of 16 and 26. According to the American Cancer Society, the exposure to HPV for most women in the United States happens before age 23 and, for many, by age 16.

"It is likely that the vaccine will be more effective if given to younger girls, before the onset of sexual activity, but we have very little data from this age group," Debbie Sanslow, the American Cancer Society's director of breast and gynecological cancers, said in a statement.

If the vaccine were approved for younger girls, dispensing it would likely be in the hands of pediatricians, not gynecologists.

Dr. Marc Childs, a pediatrician with the Carmel office of the Mount Kisco Medical Group, said if the vaccine were recommended, he would be willing to offer it, perhaps to girls ages 11, 12 or 13. He said he would point out to parents that if their daughter acquired HPV from sexual activity, she would be at high risk for cervical cancer.

"I think most parents recognize that at some point their daughter's going to be sexually active," he said.

Still, he said vaccines that have come out in the past several years have been met with increasing resistance from parents because of the fear of side effects.

"I think that's a general trend where people are tending to question vaccines much more," he said.