ATLANTA (AP) — A vaccine against cervical cancer hasn't been all that popular for girls. It may be even a harder sell for boys now that it's been recommended for them too.

A government advisory panel on Tuesday decided that the vaccine should also be given to boys, in part to help prevent the cancer-causing virus through sex.

Public health officials have tried since 2006 to get parents to have their daughters vaccinated against the human papillomavirus, or HPV, which causes most of the cervical cancer in women.

They have had limited success, hitting a number of hurdles. Some parents distrust the safety of vaccines, especially newer products. Others don't want to think about their daughters having sex one day, or worry that the vaccine essentially promotes promiscuous behavior.

Tuesday's vote by the Advisory Committee on Immunization Practices' was the first to strongly recommend routine vaccination for boys since the vaccine was first approved for them two years ago. Officials acknowledged the low rate in girls encouraged them to take a new, hard look.

Experts say a key benefit of routinely vaccinating boys could be preventing the spread of the virus to others through sex — making up somewhat for the disappointing vaccination rate in girls. But the recommendation is being framed as an important new measure against cancer in males.

"Today is another milestone in the nation's battle against cancer," said Dr. Anne Schuchat, a U.S. Centers for Disease Control and Prevention administrator who oversees the agency's immunization programs.

Federal health officials usually adopt the panel's recommendations and ask doctors and patients to follow them.

The vaccine has been advised for girls since 2006. Just 49 percent of adolescent girls have gotten at least the first of the three HPV shots. Only a third had gotten all three doses by last year.

"Pretty terrible," Schuchat said.

Schuchat attributed the low rates for girls to confusion or misunderstanding by parents that they can wait until their daughter becomes sexually active. It works best if the shots are given before a girl or boy begins having sex.

Some conservatives argue the vaccine could promote promiscuous behavior. It has come up in the GOP presidential campaign. Texas Gov. Rick Perry came under attack for a 2007 executive order requiring adolescent girls to get the vaccine (with an opt-out clause). When conservative lawmakers rebelled, he backed down.

An estimated 75 to 80 percent of men and women are infected with HPV during their life, but most don't develop symptoms or get sick, according to the CDC. Some infections lead to genital warts, cervical cancer and other cancers, including of the head and neck.

The HPV vaccine is approved for use in males and females ages 9 to 26; it is usually given to 11- and 12-year olds when they get other vaccines. The committee also recommended that males 13 to 21 years get vaccinated.

Tuesday's vote follows recent studies that show the vaccine prevents anal cancer in males, and may work against a type of throat cancer. A study that focused on gay men found it to be 75 percent effective against anal cancer.

While anal cancer has been increasing, it's still fairly rare. Only about 7,000 U.S. cases in men each year are tied to the strains targeted in the HPV vaccine. In contrast, about 15,000 vaccine-preventable cervical cancers in women occur annually.

Preventing a cancer that's primarily associated with gay men may not be much of a selling point, said Dr. Ranit Mishori, a family practice doctor in Washington, D.C. and an assistant professor at the Georgetown University School of Medicine.

Some parents may say "'Why are you vaccinating my son against anal cancer? He's not gay! He's not ever going to be gay!' I can see that will come up," said Mishori, who supports the panel's recommendation.

Schuchat indicated the CDC is ready for that kind of argument: "There's no data suggesting that offering a vaccine against HPV will change people's subsequent sexual behavior," she said.

So far, the threat of genital warts hasn't been persuasive: Some data suggest that less than 1.5 percent of adolescent males have gotten the vaccine over the past two years.

Meanwhile, some feel it's unlikely that most parents will agree to get their sons vaccinated primarily to protect girls. A survey of 600 pediatricians last year found that nearly 70 percent of doctors thought families would deem vaccination of their boys as unnecessary.

Experts at the committee meeting noted an earlier analysis that showed vaccinating boys would not be cost-effective if the female vaccination were high.

"If you do reach high coverage of females, will you stop vaccinating males?" asked Dr. David Salisbury, director immunization for the United Kingdom's Department of Health.

There are two vaccines against HPV, but Tuesday's vote applies only to Merck & Co.'s Gardasil, which costs $130 a dose. The other vaccine wasn't tested for males.

The committee's recommendation — and the greater insurance coverage of the vaccine that is expected to follow — will make it easier for more boys to get the shots, said Dr. Mark Feinberg, chief public health and science officer for Merck Vaccines.

Merck officials bristled at the idea that males would see the vaccine as mainly meant for gay men, noting that HPV-caused anal cancers can occur in heterosexual men.

Maura Robbins of Chicago said she's likely to have her 12-year-old son, Cole, vaccinated against HPV — but probably not until he's a little older. "I would just like to see some long-term testing and long-term results," she said.