If you could give your child a 70 percent likelihood of preventing cancer, would you do it? Some parents won't, or at least not soon enough to make a big difference. In a new survey of more than 9,000 moms, only 49 percent said they intended to get their daughters vaccinated against the virus (HPV) that causes cervical cancer at the recommended time: when girls are ages 9 to 12. And by the way, the HPV vaccine probably prevents most oral cancers too. But the moms still didn't say yes.

Instead, 86 percent of them intended to get their daughters vaccinated between ages 16 and 18. Kudos to the moms for understanding the importance of this breakthrough vaccine, which works to prevent the fifth most deadly cancer in the world. But waiting can be dangerous: One in four American girls has already had sex by age 15. And like a certain former president, many of them may not consider oral sex to be "sex." Or know that it is a leading cause of oral cancers.

Plenty of parents who balk at vaccinating their tweens tell us, "My 12-year-old isn't having sex." Our answer? Terrific. But the point is that she should get the vaccine before she even starts experimental petting with a boyfriend. It takes at least six months to get the three-shot series, and girls should have all three before any possible exposure to the HPV virus occurs. Also, the more people who get the vaccine, the greater the possibility that the HPV strains that cause cervical and oral cancers will vanish -- or at least be a lot harder to come in contact with. And contact is the main problem: The virus is transmitted from skin to skin, not through fluids, so you don't even have to have intercourse to get it.

Exposure is easier to come by than celebrity bikini shots: More than 6 million people get HPV infections every year (although most of them don't realize it, because it's usually symptomless). There's evidence that nearly 40 percent of women develop an HPV infection within 24 months of their first sexual experience. In fact, if you've had sex, the odds are extremely high that you (yes, you) have been infected. Up to three-quarters of people have.

Some parents put off this protection injection for fear that it will encourage their teens to be more promiscuous. But in studies, even available condoms don't make high-schoolers more likely to have sex, and it's far less likely that a series of cancer-vaccination shots would push them into it.

What if your daughter's already 13 or older? Take her in for her first vaccination now. While it's best to get the shots when they can be the most effective, the vaccine's currently approved for females up to age 26. So far, side effects seem to be minor: The shots have a reputation for hurting more than many vaccinations. Kids sometimes faint, but fainting after shots is fairly common in this age group. Afterward, there's often some swelling and redness at the shot site, and occasionally flulike symptoms occur (not uncommon with vaccinations).

Now here's what's great about the vaccine (brand name, Gardasil): It protects against the nastiest strains of HPV: types 6, 11, 16 and 18. These are linked to 70 percent of cervical cancers and 90 percent of all HPV infections. (By the way, genital warts also usually are the result of HPV 6 and 11, so that's a nifty bonus.) Studies are currently under way to see whether the vaccine is effective and useful in boys.

But don't depend on a vaccine to do the talking. You need to tell your kids how to prevent sexually transmitted infections (STIs) long before they have sex. Keep it simple, straightforward and age-appropriate. Have a sense of humor if you can muster one, but be sure you're clear when you get to the part about STIs being as readily transmitted through oral sex as intercourse. As with attempting "easy" skateboarding tricks, eating pizza that's been sitting out all night and driving over the speed limit, chances are that what kids think is safe probably isn't.

The YOU Docs -- Mike Roizen and Mehmet Oz -- can be contacted at www.RealAge.com.