Parents used to think that once their kids were out of elementary school, they were done with vaccines. But the rules are changing.

In California, middle schoolers and high schoolers now have to prove that they’re immunized against pertussis, or whooping cough, in order to attend school. It’s one of dozens of states that have recently passed laws requiring vaccines for teens and tweens.

The California law was prompted by an outbreak of whooping cough that killed 10 babies last year, and sickened 9,000 people. “It had been 63 years since we’d seen those types of numbers,” says Ron Chapman, director of the California Department of Public Health

Pertussis causes a violent cough that can last for weeks, and can be deadly in babies too young to get vaccinated. Because it spreads easily in schools, and because the protection that children get from pertussis shots in early childhood wears off, health officials vaccinate older children to help halt spread of the disease.

But that means they have to vaccinate about 3 million children. “It is a huge, massive vaccination response,” Chapman says. It also means rolling out every public health communication tool in the book, from multilingual public service announcements to Facebook posts.

Parents are targeted, too. Jeanette Restauro of Fairfield, Calif., got four different reminders to get her 11-year-old daughter vaccinated. “The first time I got the information was through my daughter’s backpack,” she says. “Then a few weeks later they did it again. Then once on the email and once in a phone recording.”

That worked: Restauro took Alyssa in to get the shot. It’s something she never had to do when her four older children were that age.

But it’s something that parents all over the country now have to start thinking about. In the past few years, dozens of states have passed laws requiring shots for teens and preteens. Pertussis (given in the Tdap shot) and meningococcus are the most common.

“It used to be that when you were in kindergarten you were done with immunization, but that’s not how it is any more,” says Sharon Humiston, a professor of pediatrics at Children’s Mercy Hospital in Kansas City, Mo. “You have immunizations throughout the lifespan now.”

Sometimes that’s because early-childhood vaccinations, like whooping cough, wear off and boosters are required. In other cases, it’s because doctors have come up with new vaccines, like HPV. But it’s not always easy to get teenagers in for these shots. One problem is that a lot of teens aren’t covered by health insurance. And many parents and kids aren’t familiar with the diseases.

Meningococcal disease is one of those. It’s a rare but deadly form of meningitis. Humiston has seen teenagers grievously ill in the emergency room from meningococcus infections, and hopes she never sees it again. “I think that once parents see a photograph of one adolescent who has lost their limbs to meningococcal disease, they end up choosing the vaccine,” she says.

That’s why the federal Centers for Disease Control and Prevention and state health departments are trying to educate tweens, teens, and their parents about both the diseases and the vaccines available. (The CDC’s preteen and teen vaccines website includes a quiz, videos, and a vaccine scheduler.)

In some cases, teenagers may need catchup vaccines for diseases such as chicken pox or hepatitis B. And as teen vaccines become more common, parents and pediatricians are learning that while big kids may not cry, they don’t always handle shots so well. Humiston says: “We even sometimes have adolescents who faint after getting their shots.”

That’s a reminder, if any is needed, that big strong 17-year-olds still need parents watching their backs when it comes to health.