JABS that protect against cervical cancer do not make girls promiscuous, says the first study to compare medical records for vaccinated and unvaccinated girls.
The researchers didn't ask girls about having sex, but instead looked at "markers" of sexual activity after vaccination against the sexually transmitted human papillomavirus, or HPV.
They examined up to three years of records on whether girls had sought birth control advice; tests for sexually transmitted diseases or pregnancy; or had become pregnant.
Very few of the girls who got the shots at age 11 or 12 had done any of those over the next three years, or by the time they were 14 or 15. Moreover, the study found no difference in rates of those markers compared with unvaccinated girls.
HPV is the leading cause of cervical cancer and the study involved nearly 1,400 girls in Atlanta, US.
Whether vaccination has any influence on similar markers of sexual activity in older teens wasn't examined in this study but other research has suggested it doesn't.
The results of the study are "comforting and reassuring," said lead author Robert Bednarczyk of Kaiser and Emory University.
Some parents have raised concerns that the shots "are a licence to have sex," but the study bolsters evidence against that concern, said experts.