A vaccine that could prevent both cervical cancer and genital warts may be available as early as next year. In a newly reported study, the vaccine was found to be 90 percent effective for preventing the majority of viral infections that cause these sexually transmitted diseases.

Experts say the highly anticipated cervical cancer vaccine could have a huge impact on the thousands of women with this cancer worldwide. About 500,000 women get cervical cancer each year, mostly in developing nations without screening programs. Half end up dying from the disease.

"This is a very exciting time," researcher Luisa L. Villa, PhD, tells WebMD. "We have shown that this vaccine is highly effective. Universal vaccination could lead to dramatic declines in cervical cancer."

100 Percent Protective Against Disease

Cervical cancer is almost exclusively caused by the human papilloma virus, or HPV. There are more than 100 types, but only certain high-risk strains cause lesions that over time can develop into cancer if not treated.

Routine screening with Pap smears can detect abnormalities and prevent cervical cancer. The widespread use of Pap smears has been shown to reduce cervical cancer rates in the U.S. It is recommended that women begin screening within three years of becoming sexually active or age 21, whichever comes first.

The HPV vaccine targets four high-risk strains of HPV -- types 16, 18, 6, and 11. About 70% of cervical cancers are caused by infection with HPV 16 and HPV 18, and 90 percent of genital warts are caused by infection with types 6 and 11.

The study, which was funded by the vaccine's manufacturer, Merck, involved 277 sexually active young women who were given the HPV vaccine and 275 sexually active women who were given a placebo vaccine. The women showed no prior abnormalities on cervical exams.

The vaccinated group received two booster shots within six months of the initial vaccination. The group was followed for three years. During that time the women had repeated Pap tests. HPV tests were also performed. HPV tests detect the DNA of cancer-causing types of HPV.

Thirty-five women in the placebo group developed persistent infection with one of the HPV strains, compared with four women who received the vaccine.

There were six diseases associated with HPV infection in the placebo group and none in the vaccine group.

The vaccine reduced persistent HPV infection by 90 percent and was 100 percent effective three years later in preventing precancerous cervical lesions and genital warts. The findings are published in the April 7 online edition of The Lancet Oncology.

The Vaccine Race Is On

Researchers are developing many vaccines to prevent different cancers, but the HPV vaccine is considered the closest to approval.

Merck is one of two drug giants racing to develop an effective and safe HPV vaccine. GlaxoSmithKline also reported promising results late last year in a study involving 1,100 young women. The vaccine used in that trial targeted HPV strains that cause cervical cancer but not genital warts.

Both Merck and GlaxoSmithKline have begun much larger trials of their respective vaccines. Villa tells WebMD that early results from Merck's investigation are expected later this year. If the trials go well, the company hopes to introduce the vaccine late in 2006, she says.

Most experts agree that the vaccine will have the most impact if given to young girls in countries that don't screen for cervical cancer and before they become sexually active.

But its impact in the U.S. and other developed nations, where cervical cancer rates are low due to screening, is unclear, says Debbie Saslow, PhD, director of breast and gynecological cancers for the American Cancer Society.

The vaccine will not replace Pap smears, she says, because the vaccine does not protect against about a dozen HPV strains that cause between 25 percent and 30 percent of cervical cancers. And there is some concern that vaccinating against the two major cervical cancer agents will lead to an increase in these other cancer-causing strains.

"This vaccine could have a huge impact if you could vaccinate young girls in countries that don't have routine cervical cancer screening," Saslow tells WebMD. "But these are the countries that are going to be least able to afford it. And within the U.S. it isn't likely that people who are not being screened will get vaccinated."

Saslow says the vaccine has a lot of potential, but there are a lot of unanswered questions about its use.

"Even if this vaccine isn't perfect, it is still very exciting to think that within a few years we may have one that really can prevent all cervical cancers," she says.

By Salynn Boyles, reviewed by Brunilda Nazario, MD

SOURCES: Villa, L. The Lancet Oncology, April 7, 2005; online publication. Luisa L. Villa, PhD, department of virology, Ludwig Institute for Cancer Research, Sao Paulo, Brazil. Debbie Saslow, PhD, director of breast and gynecological cancer, American Cancer Society, Atlanta.