DEAR DOCTOR K >> My son says that if I get a booster shot for pertussis, it will help protect his kids from getting whooping cough. That seems far-fetched to me.

DEAR READER >> It's not far-fetched. Even if you were immunized against pertussis (the bacteria that cause whooping cough) as a child, you may need a booster shot. Why? Because pertussis is highly contagious, and without a booster shot you are at some risk for getting it. And if you get it, you could pass it on to your grandkids.

Whooping cough got its name because the bacterial infection causes violent coughing. The coughing makes it hard to breathe and produces a deep "whooping" sound. Pertussis can occur at any age. If infants and young children get it, they are particularly at risk to become seriously ill.

When I went to medical school, a vaccine for pertussis was radically reducing the number of cases. It was another example of how infectious diseases were going away because of vaccines. The vaccine has, indeed, made a huge difference. But vaccines work only if people take them, and not every vaccine offers lifetime protection.

Unfortunately, many people resist getting vaccines, and the protective effects of the pertussis vaccine tend to decline over time. As a result, the number of pertussis cases in the United States has increased in recent years. There were about 17,000 reported cases in 2009; in 2014, there were nearly 33,000 cases.


To keep kids healthy, adults need to get immunized, too. That's because of something called "herd immunity." When enough people are immunized against a disease, it becomes uncommon — simply because the immunized people can't catch it, and therefore can't spread it.

Herd immunity helps to protect:

• Small children, especially infants, who either are too young to be immunized or haven't had enough doses to be fully protected.

• People who have problems with their immune systems, many of whom can't get vaccines, and all of whom are more susceptible to infections.

Herd immunity works when enough people are immunized. The Centers for Disease Control and Prevention (CDC) recommends that adults get a Tdap vaccine (which protects against pertussis, along with tetanus and diphtheria) in place of one of their regular tetanus boosters (the Td shot that is recommended for adults every 10 years).

You can get the Tdap vaccine no matter when you last received a Td shot. Getting vaccinated with Tdap at least two weeks before coming into close contact with an infant is especially important.

By getting a Tdap vaccine, you'll be helping to keep your grandkids healthy.

Dr. Komaroff is a physician and professor at Harvard Medical School.