SUNDAY, May 4 (HealthDay News) -- New research shows that only half of American mothers intend to have their teenaged daughters vaccinated against human papillomavirus (HPV) if the girls are under the age of 13, despite government guidelines that suggest the opposite.

HPV, which is sexually transmitted, is the primary cause of cervical cancer. The first vaccine against the virus, Gardasil, was approved in 2006. The U.S. Centers for Disease Control and Prevention currently recommends that 11- and 12-year-old girls be targeted for this vaccine, as most girls of this age are not yet sexually active, have not yet been exposed to HPV, and will therefore achieve maximum protection.

However, this study suggests that many mothers aren't willing to follow those recommendations.

"Mothers had a lower intention to vaccinate [younger] daughters," said study author Dr. Jessica Kahn, an associate professor of pediatrics at Cincinnati Children's Hospital Medical Center. "This presents a challenge, and provides us with an opportunity to educate mothers about the importance of vaccinating girls under 13 years of age because the vaccine will have a greater health impact if given before 13."

Kahn will present the findings Sunday at the Pediatric Academic Societies' annual meeting in Honolulu.

About 10,000 new cases of cervical cancer are diagnosed in the United States each year, with about 4,000 women dying of the disease annually.

Three-quarters of U.S. women will be exposed to HPV at some point in their lifetime and, at any one time, one-quarter have been infected.

According to one estimate, giving the vaccine universally would eliminate about 70 percent of cervical cancer cases. Gardasil protects against most, but not all, types of HPV that cause cervical cancer.

This study is the first national survey of its kind and also the first to measure attitudes towards the vaccine since it was approved by the U.S. Food and Drug Administration in 2006.

Forty-nine percent of almost 10,000 respondents intended to vaccinate a daughter if she were 9 to 12 years old; 68 percent intended to vaccinate if the daughter was 13 to 15 years old; and 86 percent said they would vaccinate if the daughter was 16 to 18 years of age.

Specific beliefs about HPV vaccine were the most powerful predictor of one's intention to vaccinate one's 9-to-12-year-old daughter.

The belief that really stood out was that the vaccine would protect the daughter against cervical cancer. "That was not at all surprising to me," Kahn said. "[Other] studies have shown that the most powerful factor driving mothers' decisions is the desire to protect a child from harm."

The next most powerful predictor were beliefs that the vaccinations would not cause a child to engage in riskier sexual behaviors.

"That implies we need some studies to prove or disprove this concern," Kahn said. "It also is going to be important for clinicians to address that head on with parents."

If a clinician recommended the vaccine, the mom was more likely to decide to vaccinate her daughter.

Mothers were also more likely to go for the vaccine if they thought their daughter was at risk for HPV.

All of these factors could be incorporated into messages, including those seen in brochures and posters about HPV and the vaccine, Kahn said. She was also lead author of a paper appearing in the May issue of Obstetrics & Gynecology that found that interventions which address personal beliefs about the HPV vaccine as well as system-wide barriers to vaccination could lead to higher vaccination rates.

"This shows that there's a difficulty in having mothers recognize that their children will become sexually active at a relatively young age," said Dr. Jay Brooks, chairman of hematology/oncology at Ochsner Health System in Baton Rouge, La. "It's a process and it's an attitudinal change that has to occur."

More information

The U.S. National Cancer Institute has more on HPV and cervical cancer.