If you're the parent of a " 'tween" daughter, your family physician may have recommended vaccinating her against the human papillomavirus, or HPV, a sexually transmitted disease that can cause cervical cancer.

But how much do you really know about this new vaccine?

"I do not think that the public understands all the potential benefits of HPV vaccination, including the protection it may offer against vulvar cancer, vaginal cancer, anal cancer, and head and neck cancers," said Dr. Jessica Kahn, associate professor of pediatrics in the Division of Adolescent Medicine at Cincinnati Children's Hospital Medical Center.

The U.S. Food and Drug Administration approved the HPV vaccine, called Gardasil, in June 2006, to prevent precancerous conditions of the cervix.

As a result, "vaccine marketing strategies have not focused on the potential for the vaccine to prevent other cancers, and in both men and women," Kahn explained. In addition, many people do not understand the link between HPV and other cancers that affect both sexes, such as head and neck malignancies, she added.

HPV is the most common sexually transmitted infection in the United States, accounting for the majority of cases of cervical cancer. At least 50 percent of sexually active people will get HPV at some point in their lives, according to the U.S. Centers for Disease Control and Prevention.

While HPV usually goes away on its own, sometimes it lingers and continues to change the cells in a woman's cervix. Without treatments, these changes can lead to cancer. What's more, HPV has been linked to genital warts and to less common cancers, including vulvar, vaginal, anal and head and neck cancers.

Ideally, the vaccine should be given before a young woman becomes sexually active, health officials say. Studies show Gardasil is nearly 100 percent effective in preventing diseases caused by the four types of HPV covered by the vaccine — the types associated with the most cases of cervical cancer and genital warts. But it does not treat existing HPV infections, genital warts, pre-cancers or cancers. Nor does it cover every type of HPV, and there are more than 200 types.

"I have several young ladies who are under the care of gynecology because of their exposure to HPV and cervical changes," said Dr. Susanne Tropez-Sims, an associate dean and professor of pediatrics at Meharry Medical College in Nashville, Tenn.

Gardasil's approval almost two years ago ignited concern that vaccinating young women would promote sexual promiscuity. A bigger issue, though, has been the fact that it's a new vaccine, said Dr. Kristen Feemster, a program scholar with The Robert Wood Johnson Clinical Scholars Program at the University of Pennsylvania, whose interests include vaccine policy.

Parents want to make sure it's safe for their daughters, Feemster said, "and certainly all of the data show that it is an extremely safe vaccine."

Reports to the Vaccine Adverse Event Reporting System, a joint CDC-FDA effort to collect information on possible side effects of vaccination, suggest the most common complaint is soreness at the site of vaccination. There have been cases of fainting after vaccination, as well.

More troubling, four deaths have been reported in women who received the vaccine. However, the CDC said none of the deaths appeared to be caused by vaccination. There have also been 13 unconfirmed cases of Guillain-Barre syndrome, a neurological disorder that can lead to paralysis.

"Even if a young woman becomes ill after receiving a vaccine, the illness is not necessarily related to vaccination, and this appears to be the case with respect to" these cases, Kahn said.

Parents and young women are very receptive to the HPV vaccine when physicians take the time to explain what is known about the vaccine — and what is not, such as whether booster shots may be needed in the future, Tropez-Sims said. All but one of her patients have agreed to be vaccinated.

"I believe when people dissent against the vaccine, they don't fully understand the potential for prevention of disease," she said.

The CDC's Advisory Committee on Immunization Practices recommends giving the vaccine routinely to girls 11 to 12 years of age. Healthcare providers, at their discretion, may give it to girls as young as 9.

The HPV vaccine joins a small cadre of vaccines recommended for adolescents. These include a combined tetanus, diphtheria and pertussis vaccine, and a vaccine against meningococcal disease, the leading cause of bacterial meningitis.

And like other vaccines that ward off disease, there's data to suggest that the HPV vaccine should be given broadly, not just to sexually active teens.

"I like to think of it as part of the whole prevention package for early adolescents that will keep them protected," Feemster said.

LEARN MORE:

www.cdc.gov/std/hpv/STDFact-HPV-vaccine.htm, Centers for Disease Control and Prevention's site on sexually transmitted diseases.