ATLANTA (AP) ― Only about half of the teenage girls in the U.S. have rolled up their sleeves for a controversial vaccine against cervical cancer - a rate well below those for two other vaccinations aimed at adolescents.

The vaccine hit the market in 2006. By last year, just 49 percent of girls had gotten at least the first of the recommended three shots for human papilloma virus, or HPV, a sexually-transmitted bug that can cause cervical cancer and genital warts. Only a third had gotten all three doses, the Centers for Disease Control and Prevention said Thursday.

In contrast, the CDC said about two-thirds of teens had gotten the recommended shot for one type of bacterial meningitis and a shot for meningitis and tetanus, diphtheria and whooping cough.

Granted, it can take many years for a new vaccine to catch on and reach the 90 percent and above range for many longstanding childhood vaccines. But use of HPV vaccine has been “very disappointing” compared to other newer vaccines, said the CDC’s Dr. Melinda Wharton.

“If we don’t do a much better job, we’re leaving another generation vulnerable to cervical cancer later in life,” said Wharton.

Why aren’t more girls getting HPV shots? The vaccine can be very expensive, and it can be a bit of a hassle. It takes three visits to the doctor over six months.

But sex no doubt has something to do with it, experts said.

Girls are supposed to start the series when they are 11 or 12 - before most girls become sexually active. The vaccine only works if a girl is vaccinated before she’s first exposed to the virus.

But some parents may misunderstand, thinking their daughters don’t need it at such a young age because they aren’t sexually active. Others may believe that it would require a discussion about sex and sexuality - a talk they may not feel ready to have, some experts said.

The government needs to be more aggressive about changing those perceptions with a major education campaign, Jeff Levi, executive director of the Trust for America’s Health, a Washington, D.C.-based research group, said in a statement.

Millions of Americans - women and men - become infected with HPV each year, though most show no symptoms and clear the virus on their own. But some strains persist and can cause genital warts and cancer. About 12,000 women are diagnosed with cervical cancer each year, and about 4,000 die from it, according to CDC statistics.

The new study was based on a 2010 telephone survey of the parents of more than 19,000 adolescents ages 13 to 17, who allowed researchers to check their kids’ vaccination records.

Rhode Island and Washington had the highest HPV vaccination rates, both around 70 percent for at least one shot. Idaho had the lowest rates, at about 29 percent.

The study was published online in a CDC publication, Morbidity and Mortality Weekly Report.