Like many other grown-ups, I hadn’t given any thought to what we used to call the D.P.T. vaccine — for diphtheria, pertussis and tetanus — for decades. I got the shots when I was a child, and I made sure my daughter got them during her childhood immunizations. Every now and then, my doctor tells me it’s time for a tetanus booster, so I get one. That’s enough, right?

The Centers for Disease Control and Prevention is advising otherwise. In recent years, the federal agency been steadily expanding its recommendations for the age groups that should receive a single dose of what’s now known as T.D.A.P., short for tetanus, diphtheria and acellular pertussis.

First its advisory committee on immunization recommended the vaccine for adolescents, then for all adults through age 64. (In this case, as in others, older adults were initially excluded from clinical trials. This practice really has to stop.)

Now the Food and Drug Administration has approved one brand of T.D.A.P., called Boostrix, for adults over age 65. Accordingly, the C.D.C. has issued guidelines recommending the vaccine for those older adults “who have or who anticipate having close contact with an infant aged less than 12 months,” as well as for all health care providers.

Doting grandparents of newborns and about-to-become-grandparents: This means you. When the C.D.C. advisers next meet in February, they may recommend vaccination for all older adults.

We’ve managed to virtually eliminate diphtheria in the United States, Tom Clark, a C.D.C. epidemiologist, told me in an interview; the last confirmed case was in 2003. Tetanus has also become rare: 30 to 50 cases a year, mostly in adults over 65 who didn’t complete their vaccinations or haven’t kept up with boosters.

While we all want to continue holding those once-lethal diseases at bay, the real worry here is pertussis, a k a whooping cough. “Anyone can get pertussis. It’s not just a childhood disease,” Dr. Clark said. Last year, the C.D.C. recorded 27,550 cases, and that probably is an underestimate.

This illness, characterized by extreme coughing fits that recur for four to six weeks, is among those that are milder in older people but more dangerous to the very young. Older people can crack a rib or rupture a blood vessel from coughing; babies usually are hospitalized, and last year 25 infants died.

“When very young infants get pertussis, it’s usually from someone in their own households,” Dr. Clark said. Public health specialists are hoping that concern for their grandchildren will lead a lot of older adults to get vaccinated, which keeps everyone safer.

As often happens with new vaccination guidelines, it takes some time for the word to spread. Physicians may not mention vaccination for us or our parents, but we can raise the subject ourselves. The vaccine’s only common side effect: “It gives a lot of people sore arms,” Dr. Clark said. But the pain at the injection site ebbs in two or three days.

Another potential problem: T.D.A.P. vaccine is covered by Medicare Part D, which means doctors can’t simply add it to their bills under Part B. Either people have to pay out of pocket and await reimbursement, or they can go to pharmacies that will bill Medicare directly. At least T.D.A.P. isn’t a terribly expensive vaccine; it retails for $35 to $40, plus the cost of the injection.

That sets it apart from Zostavax, the shingles vaccine, which goes for about $200 and is also covered under Part D. I know two people in their 90s currently suffering — and that’s the right word — from shingles, so let me rant about this subject once more. The pain of paying for the vaccine, if you can possibly manage it, is not nearly as severe as the pain of this viral disease, which that takes a far worse toll on the elderly than on the young. The vaccine is now F.D.A.-approved for adults over 50, and while shortages persist, the supply has improved, says Merck, the company that makes it.

As for T.D.A.P., it can be administered at the same time as a flu shot, which most older adults get at this time of year. So there’s an opportunity.