Researchers in the North America and Brazil have successfully tested a vaccine to prevent cervical cancer, the second most common cancer in women around the world, after breast cancer. Such a vaccine might eventually prevent hundreds of thousands of deaths each year.
The human papillomavirus is a common infection that invades more than 75 percent of women at some time in their lives. Most of the time, it lasts only a short time and produces no symptoms. But in nearly 500,000 women worldwide each year, it persists long enough to cause cancer of the cervix, the opening to the uterus. Nearly 250,000 die from it each year, most of them in developing countries.
An experimental GlaxoSmithKline vaccine offers hope against this disease.
Researchers tested it for two-and-a-half years in more than 1100 U.S., Brazilian, and Canadian women aged 15 to 25. According to the journal Lancet, three doses of the vaccine prevented human papillomavirus infections in 92 percent of the women. Even better, it completely prevented the long-lasting infections that can lead to cancer.
"It is outstanding, phenomenal news that it is 100 percent! We are so excited with that outcome," said study leader, Dartmouth University Medical School researcher Diane Harper.
She added that the vaccine proved safe with few side effects.
"This really moves women's health care forward in a very positive direction and allows us to make changes in the way we care for women at a personal level," she added.
The vaccine is based on a molecule developed by the U.S. government's National Institutes of Health, NIH. It was engineered to consist only of the protein outer shell of two strains of the human papillomavirus, but carries none of the infectious matter normally found within the virus, so it cannot infect a person. The human immune system recognizes this shell as an invader and develops antibodies to fight it, thereby mobilizing the body against a real infection.
The two strains of the virus incorporated by the vaccine are linked to about 70 percent of cervical cancers worldwide. Having a widely effective cervical cancer vaccine is considered important for poor countries where a common diagnostic technique called a Pap smear, is too expensive. In a Pap smear, cells from the lining of the cervix are removed with a cotton swab and examined under a microscope for cancer of precancerous changes.
Physician Christopher Crum of Brigham and Women's Hospital in Boston says industrial countries would benefit, too, because fewer of these expensive examinations would be needed.
"If the vaccine were to work, you would see a reduction in abnormal Pap smears, a reduction in cancers, and you would see a redefinition of cervical cancer risk and very likely the way in which it would be managed," he noted.
At Dartmouth University, researcher Diane Harper says the vaccine will be tested in an even larger worldwide population of 15,000 women before it is submitted to government regulatory authorities for approval.
"My guess will be that we'll have a vaccine ready for an entire population certainly by 2010," she explained.
University of Helsinki doctors agree that regulatory approval of a vaccine against human papillomavirus is not far away. In a commentary accompanying the Lancet study, they say it will probably be the first licensed vaccine against a common sexually transmitted infection.
Diane Harper notes that a final version of the vaccine might incorporate two or three more human papillomavirus strains, but that adding more would not be cost effective. Dr. Crum in Boston says if women were to be inoculated against all of the most important strains before becoming sexually active, the risk of cervical cancer would drop at least 85 percent.
"There are as many as 15 or 20 human papillomaviruses that can cause cervical cancer," said Dr. Crum. "But most of these cancers fall under the purview of just a few viruses. Thus, it might be possible some time in the future to tailor a vaccine that might cover at least a significant proportion of those associated with cervical cancer."
Such a vaccine could also stop other harm done by the virus, including genital warts in men and women and rare forms of penile, anal, vaginal, and oral cancer. Researchers say the vaccine might also be taken by men to keep them from infecting their female partners.