You’ve probably heard all about the controversy over the vaccine for the human papillomavirus (HPV) that is given to children shortly before their teen years to prevent cancer, but something that scientists discovered was pretty surprising: parents’ resistance to the vaccine can be dramatically reduced by simply making it not mandatory.

The broader anti-vaccination movement has campaigned against the HPV vaccine, even though most scientists regard the vaccine as safe and effective, and as a result just one in five parents support a mandatory HPV vaccine in order for a child to attend school. But, the study showed that parents would in fact be comfortable with the vaccine if parents weren’t required to give it to their children, according to a UNC Lineberger Comprehensive Cancer Center statement.

And the increase was dramatic: parents were three times more likely to support the vaccine if it wasn’t mandatory. However, making the vaccine optional makes compliance — necessary for a vaccine to be effective — a big problem for authorities, so they have to weigh that option with going the more difficult but more effective route of trying to convince the public to make it mandatory.

The Centers for Disease Control and Prevention recommends the vaccine for girls and boys at the ages of 11 and 12, as it can help fight cervical cancer and has a strong safety record.

“School entry requirements are highly acceptable to parents, but only when implemented in a way that makes them ineffective,” said the study’s senior author Noel Brewer, PhD, a member of the University of North Carolina Lineberger Comprehensive Cancer Center and an associate professor in the UNC Gillings School of Global Public Health. “Opt-outs lead to a large number of parents choosing not to vaccinate their children, and that makes requirements ineffective in raising vaccination rates.”