"FDA approval of the HPV vaccine, the first vaccine targeted specifically to preventing cancer, is one of the most important advances in women's health in recent years," states the American Cancer Society in a news release.
The vaccine protects against infection from four strains of the human papilloma virus, or HPV. Two of these strains, HPV-16 and HPV-18, account for about 70 percent of cervical cancers. The other two strains covered by the vaccine, HPV- 6 and HPV-11, account for about 90 percent of genital warts.
"Gardasil is a major health breakthrough -- the first vaccine specifically designed to prevent cancer -- and is approved to prevent not only cervical cancer but also genital warts," says Kevin Ault, MD, leader of Gardasil clinical trials at Atlanta's Emory University, in a Merck news release.
The vaccine is approved for 9- to 26-year-old girls and women. While it is almost always females who get HPV-related cancer, the virus is spread by both men and women during sexual contact. And both men and women are susceptible to genital and rectal warts, which can lead to cervical changes and abnormal Pap smears in women.
Gardasil is not approved for use by boys and men. Clinical trials evaluating Gardasil vaccination of boys and men are underway, a Merck spokesperson tells WebMD.
Effective and Safe
In clinical trials reported so far, the vaccine has been extremely effective. It appears to be 100 percent effective in protecting against the HPV-16 and HPV-18 strains. It also seems extremely safe. One reason is that the vaccine isn't a live virus, but a virus-like particle. This means it's an empty shell, with immunity-stimulating particles on the outside and no viral machinery on the inside.
HPV expert Jessica Kahn M.D., MPH, associate professor of pediatrics at Cincinnati Children's Hospital Medical Center, says she's planning to have her teenage daughter vaccinated.
"What we parents most want to know about the vaccine is whether it is safe, and whether it is effective," Kahn tells WebMD. "All data show it to be one of the safest vaccines ever tested. And it is highly effective."
To be effective, Gardasil must be given in three doses over six months (the second dose is given two months after the first; the third dose six months after the first). It's not yet clear whether a person will receive lifelong immunity. In tests checking for presence of the virus so far, the vaccines remain protective for four years and counting.
For preventing vaginal and vulvar cancer, the vaccines have been protective for at least two years. The wholesale price for Gardasil will be $120 per dose; $360 for all three doses.
There's a second vaccine in the works: Cervarix, from GlaxoSmithKline. Cervarix targets only two HPV strains, HPV-16 and HPV-18, the ones most commonly linked to cancer as opposed to genital warts.
GlaxoSmithKline says it plans to seek FDA approval for Cervarix by the end of the year. Early studies find that this vaccine, too, is extremely safe and effective.
Both Merck and GlaxoSmithKline are WebMD sponsors.
Pap Screening Still Needed
Despite its potency, Gardasil won't prevent every cervical cancer or every HPV infection. There are some 100 HPV strains out there. Those covered by the vaccine are the worst offenders, but not the only ones.
Neither Gardasil nor Cervarix prevent disease in people already infected with the virus. Perhaps as many as 80 percent of adults have been exposed to at least one strain of HPV, Kahn says. For reasons not fully understood, only a minority of people with HPV get cervical cancer or warts.
"These vaccines only prevent infection. They do not prevent disease once you are already infected with the virus," Kahn says. "The vaccines do not treat precancerous conditions."
This means that while the vaccines undoubtedly will prevent many of the annual 3,700 U.S. and 233,000 worldwide cervical-cancer deaths, it will not end cervical cancer, genital warts, or the spread of other HPVs.
"One of the points I am going to try to get across to teens is to stress that even after getting the vaccine, they must continue to get regular Pap screening," Kahn says. "Some vaccinated women will still have abnormal Pap tests. It does not mean the vaccine is not working. A lot of abnormal Paps are caused by HPVs that are not in the vaccines."
The Role of Parents
Vaccines don't work if people don't use them. Researchers think the vaccines will work best if given to teens before they become sexually active -- that is, at ages 11 to 13.
HPV is a sexually transmitted disease. Will parents object to vaccinating their teens?
Some will -- but the vast majority won't, predicts Gregory D. Zimet, Ph.D., professor of pediatrics and clinical psychology at Indiana University School of Medicine, Indianapolis. Zimet has studied parental attitudes toward vaccines, including vaccines that would protect against sexually transmitted diseases.
"There has been this idea that giving an HPV vaccine to teens might be seen by parents as giving their daughters permission to have sex -- or that it might lower some kind of barrier and lead to a sense of safety that would lead that young adolescent to engage in sex that they would not otherwise have," Zimet tells WebMD.
But when Zimet and colleagues asked parents what their concerns would be about an STD vaccine, this wasn't a common opinion. Instead, parents wanted to know how safe the vaccine was, how well it worked, and whether the disease it prevented was serious.
"There had been some concern that doctors might be reluctant to prescribe STD vaccines because of anticipated parental opposition," Zimet says. "But research indicates parents have great eagerness to have their children vaccinated against these diseases."
SOURCES Longworth, M.S. Microbiology and Molecular Biology Reviews, June 2004; vol 68: pp 362–372. Jessica Kahn, MD, MPH, associate professor of pediatrics, Cincinnati Children's Hospital Medical Center, Ohio. Gregory D. Zimet, PhD, professor of pediatrics and clinical psychology, Indiana University School of Medicine, Indianapolis. News release, American Cancer Society.
By By Daniel J. DeNoon
Reviewed by Michael W. Smith, M.D.
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