Got a new grandkid? Get vaccinated against whooping cough.

Are you preparing for the arrival of a new grandchild? If so, make sure you’re vaccinated against pertussis, also known as whooping cough. Why? Well, pertussisis a highly contagious disease that can be deadly in infants—and kids can’t get their first vaccination shot against the disease until they are at least 6 weeks old, and the full series until they are 18 months old, making them especially vulnerable. And some older people may have a mild form of the disease and not even know it, meaning they could transmit it to a new grandchild through a cough or sneeze, or even by blowing a kiss.

“The source of the pertussis bug is family members, because they get it and bring it to the infant,” says William Schaffner, M.D., professor of preventive medicine at Vanderbilt University School of Medicine in Nashville, Tenn. The best way to protect infants, he says, is to make sure everyone who touches them has been vaccinated. “The concept is to create a cocoon of protection around that infant,” Schaffner says.

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Older adults are particularly likely to be carriers of the disease in part because they may have been vaccinated against the disease many years ago, so their protection against the disease may have waned. In addition, there have been several outbreaks of the disease among not only children but also adults in recent years, making it more likely that they’ve been exposed to it. So far this year 9,768 pertussis cases have been reported to the Centers for Disease Control and Prevention, still below the 48,277 reported in 2012 (the most since 1955), but still well above average.

The outbreaks are occurring in part because the current pertussis vaccine appears to lose its protective ability over time, and in part because some people are failing to get vaccinated.

To ensure maximum immunity, all adults should make sure they’re up to date. Ask your doctor whether you’ve received the Tdap booster shoot (which protects against not only pertussis, but also tetanus and diphtheria). “If you’re not sure or don’t remember, or it was just a long time ago, you should get it again,” says Marvin M. Lipman, M.D., Consumer Reports’ chief medical adviser. “It’s the best way to make sure you and everyone around you is protected.”

—Lauren Cooper