New data shows a vaccine against the virus that causes cervical cancer partially blocks infection by 10 strains of the virus on top of the four types the vaccine targets.

That boosts protection — at least partially — to 90 percent of strains causing the deadly cancer, according to data presented Wednesday at a medical conference by Merck & Co., maker of Gardasil.

Whitehouse Station-based Merck called it the first evidence of any vaccine providing cross-protection against other strains of the human papilloma virus, or HPV.

Dr. Stephanie Blank, a gynecologic oncologist at the NYU Cancer Institute, said the finding could encourage more widespread use of Gardasil in developing countries, where some of the additional strains are more widespread and women rarely get Pap smears to detect early, curable cancers.

"That could be huge," Blank said.

Gardasil is the only cervical cancer vaccine on the market, approved for sale in 85 countries and pending approval in 40 more; it has racked up about $1 billion in sales since its June 2006 U.S. launch. GlaxoSmithKline PLC is awaiting approval of its own vaccine, Cervarix.

There are more than 60 strains of the HPV virus. About 15 are thought to cause cervical cancer; Gardasil protects against 12 of those, plus another two that cause genital warts but not cancer.

Two strains cause 70 percent of cervical cancer. Merck studies following 17,600 young women for three years found the vaccine to be 99 percent effective in blocking those strains.

New analysis of that data shows the vaccine reduced incidence of HPV-caused precancerous lesions by nearly two-thirds for the three next most common HPV strains in North America. While those three strains are less common elsewhere, together they cause about 11 percent of cervical cancer worldwide.

"There's the potential for an additional 30,000 to 40,000 cancer cases being prevented each year," mostly in developing countries, based on preliminary estimates and widespread vaccination in those regions, said Dr. Eliav Barr, head of Merck's research on infectious disease and vaccines.

There are 9,710 new cases of cervical cancer and 3,700 deaths in the U.S. each year. Worldwide, there are nearly 500,000 new cases and 233,000 deaths a year.

Dr. Jonathan Berek, chairman of obstetrics and gynecology at Stanford University School of Medicine, said he expected Gardasil to provide some protection against HPV strains not directly targeted by the vaccine, but not as much as the data shows.

"It's a reason why we should try to introduce it more broadly around the world," Berek said.

Dr. Michael Segarra of North Brunswick Pediatrics said women still need to get regular Pap smears because the vaccine doesn't cover all HPV strains, but that the extended protection will reduce anxiety in years to come as fewer women get abnormal Pap test results requiring additional testing.

Roughly 2.5 million such follow-up exams and biopsies are done each year in this country, at a cost of about $320 each.

"Any time you can reduce the possibility of getting cancer, it's very significant," added Segarra, who is vice president of the American Academy of Pediatrics New Jersey chapter.

However, Merck took heat for a behind-the-scenes campaign to get states to require sixth-grade girls to get the HPV vaccine to attend school. Merck has since dropped that campaign.