WASHINGTON - Backpack. Notebooks. Whooping cough shot?

If you haven't worried about back-to-school shots since your tween or teen was entering kindergarten, better put vaccines on the to-do list.

Older kids need a few new immunizations starting at age 11, including a shot to guard against the worrisome resurgence of whooping cough. And for the first time this year, 16-year-olds are supposed to get a booster shot, too, for a scary type of meningitis.

Many slip through the cracks. One reason: Schools don't require adolescents to comply with a list of national vaccine recommendations like they do kindergarteners.

Another reason: "Kids this age go to the doctor much less," says Dr. Melinda Wharton of the Centers for Disease Control and Prevention, who had to scramble to get her own daughter that meningitis shot before she headed to college.

"This whole back-to-school push is a good time for parents to think about their kids in terms of what vaccines are recommended."

But when it comes to whooping cough, a growing number of states are requiring updated shots as students enter middle school and beyond. A new California law requires a staggering 3 million students to show proof they're protected as they head back to class.

"It is that kind of effort that's going to help us stem the outbreaks," says Dr. Mark Sawyer of the University of California, San Diego.

Aside from an annual flu vaccine, here are federal recommendations for preteens and teens:

• A Tdap shot between ages 11 and 12. It protects against tetanus, diphtheria and pertussis or whooping cough - and the latter is key as the cough that's so strong it can break a rib is on the rise.

Young children get vaccinated before kindergarten but that protection wears off, and pertussis outbreaks in middle or high school no longer are rare. While older kids usually recover, whooping cough can cause weeks of misery - and worse, they can easily spread the bacterial infection to not-yet-vaccinated infants, who can die.

Last year was especially bad for whooping cough, with more than 21,000 U.S. cases and at least 26 deaths. California was hard hit with more than 9,200 cases - the most since 1947 - and 10 babies died.

The new California law aims to ensure everyone entering seventh through 12th grade got a booster at some point. Before the law, about half those students were estimated to be unprotected, says Dr. John Talarico of the California Department of Public Health. With vaccine vans parked at schools and special Tdap lines at some county health departments, an immunization program for the poor and underinsured has been distributing three to seven times more shots than usual in recent months, he says.

• A first dose of what's called meningococcal conjugate vaccine between ages 11 and 12, with a booster dose at 16.

This fast-moving bacteria can cause meningitis or a bloodstream infection. It's fortunately rare, causing fewer than 2,000 cases a year. But it can be so aggressive that someone can feel fine one day and be dead the next - and its main targets are adolescents and college freshmen. Why? That's not clear, but about 10 percent of the population carries the germ harmlessly in their noses and throats. Carriers tend to spread it by coughing, kissing and sharing drinking glasses, especially in crowded conditions like dormitories.

Infection initially mimics a stomach bug, with fever and vomiting. Up to 15 percent of patients die. One in five survivors suffers permanent disabilities including brain damage, deafness or amputated limbs.

CDC's statistics show that 54 percent of 13- to 17-year-olds had gotten vaccinated by 2009. But the booster dose is new advice - scientists only recently learned that that first dose wears off after five years. So if your child didn't get vaccinated until, say, 13 and now is 18 and heading for college, Wharton says don't forget the booster.

• Finally for girls ages 11 to 12, there's the HPV vaccine for strains of human papillomavirus that can cause cervical cancer. The idea is to start the three doses needed early enough to be fully vaccinated well before the girl becomes sexually active. But in 2009, only 27 percent of girls ages 13 to 17 had gotten all three doses.

"We were very disappointed in those numbers," Wharton says.

A vaccine version is sold for boys to prevent HPV-caused genital warts, although CDC hasn't yet recommended its routine use.

Wharton's final advice: Adolescence is a good time to catch up on any shots that were recommended after your child started kindergarten and thus missed, like the second dose of chickenpox vaccine that became routine for the 5-year-old set just a few years ago.

Lauran Neergaard covers health and medical issues for The Associated Press.