(Reuters Health) - State laws designed to increase teen vaccination against the cancer-causing human papillomavirus (HPV) don’t appear to influence adolescents’ choices about whether to become sexually active or use condoms, a U.S. study suggests.

HPV is among the most common sexually transmitted diseases. Most infections don’t cause symptoms and go away on their own, but the virus can cause cancers of the cervix, penis and throat.

While the U.S. Centers of Disease Control and Prevention recommends routine HPV vaccination for girls and boys starting at age 11, less than half of girls and even fewer boys are fully vaccinated against the virus, researchers write in Pediatrics. Currently, 23 states and the District of Columbia have passed legislation designed to boost vaccination rates by providing HPV education in schools, requiring insurers to provide low-cost or free shots and making vaccination mandatory, the study authors note.

These policies have been controversial, and vaccination rates remain stubbornly low, at least in part because some parents worry that giving children the HPV vaccine will encourage them to have sex too soon or without condoms.

The current study results should put these concerns to rest, said lead author Erin Cook, who completed the research at the Harvard T.H. Chan School of Public Health in Boston.

“Parents should not be concerned about legislative policies regarding HPV that have been passed so far influencing teen sexual behaviors,” Cook said by email.

For the study, researchers examined survey data collected from 886,981 high school students across the country from 2001 to 2015.

Overall, roughly one in four of the teens surveyed reported having sex at least once in the previous three months. And, 97 percent of these sexually active teens said they used condoms the last time they had sex.

To see if HPV vaccination laws might impact teens’ behavior, researchers compared the proportion of teens having sex and using condoms after these laws were passed in their states to what happened beforehand. They also looked at trends in states without any HPV vaccine laws on the books.

Across all states, the proportion of teens who said they were sexually active decreased slightly after 2007 when the HPV vaccine first became widely available, the study found.

The proportion of students having sex and using condoms was similar for states with and without HPV legislation. Moreover, there was no difference in risky sexual behavior between states with and without vaccine laws.

It’s possible this might be due to the limited scope of HPV legislation in some states, researchers note. In some places, parents can opt out of vaccination mandates, for example, and in other instances legislation provides only for education about HPV and the vaccine.

“At this time states require consent from parents for this vaccine,” said Dr. Cora Collette Breuner, a professor of pediatrics and adolescent medicine at the University of Washington and Seattle Children’s Hospital.

“If we could ask teens if they didn’t want to get cancer later in life, they would most likely say ‘no I don’t want to get cancer,’” Breuner, who wasn’t involved in the study, said by email.

However, the study wasn’t a controlled experiment designed to prove whether or how HPV vaccination laws, or getting vaccinated, might directly impact teens’ sexual behavior.

Parents should still be reassured that the study adds to growing evidence that the vaccine won’t encourage teens to start having sex or stop using condoms.

“Getting vaccinated won’t make them more prone to be more sexually active,” Breuner said. “The HPV vaccine prevents a life-threatening disease!”

SOURCE: bit.ly/2MlZdK8 Pediatrics, online August 13, 2018.