Two studies appearing this week in the New England Journal of Medicine confirm that a new vaccine is effective in preventing cervical cancer, a disease that kills almost 300,000 women around the world each year.  But some observers worry that many unanswered questions still surround the new vaccine. VOA's Jessica Berman reports.

When it was approved by U.S. regulators a year ago, health officials were very excited about what was billed as the first cancer vaccine. 

The drug, called Gardisil, protects women and young girls against four types, out of 15, of the sexually-transmitted human papilloma virus (HPV) including two aggressive cancer-causing types.

Now, two international studies involving thousands of women in 16 countries
have reached a similar conclusion. 

Kevin Ault is a professor of gynecology and obstetrics at Emory University in the US state of Georgia, and co-author of one of the two, three year studies which involved 5,400 women between the ages of 16 and 24.

"We found that we had 98 percent protection against the precancerous changes caused by those two types," he said.

Overall, the studies show that the vaccine is highly effective for women who have never been exposed to HPV.   The effectiveness drops by half, however, among women who are sexually active and may have been exposed to HPV.

But Ault says the vaccine is more beneficial than the numbers would now suggest.

"In the study, we found that 75 percent of women had not been exposed to any four types in the vaccine, and we were studying women in their late adolescence and twenties who were sexually active," he added.  "So, you know it depends upon whether you look at a glass half empty or half full."

In the second study published in the New England Journal, researchers also found the vaccine to be extremely effective in protecting selected groups of women against HPV.

But Karen Smith-McCune, a gynecologist at the University of California in San Francisco, says she is troubled by another finding:

Roughly 17 percent of vaccinated women in the study developed precancerous changes.  Gardisil targets two of the most aggressive HPV types that are responsible for 70 percent of cervical cancers. 

Smith-McCune says that leaves 15 other HPV types with the potential to cause cervical cancer.

"One of the unknowns still is whether vaccination will alter the behavior in any way of the remaining non-vaccine types of HPV," she noted.

Experts agree that for the time being, the vaccine won't replace the need for annual screening exams to look for precancerous changes that might be caused by the other 15 HPV types.