December 16, 2018
Girl coughing into her arm.

Why My Vaccinated Daughter Got Pertussis Anyway

by Amanda Z. Naprawa  

This fall, my 9-year-old daughter Olivia developed a cough. Given that she’s in fourth grade and is constantly coming home with one bug or another, we didn’t think much of it. After all, a few of her best friends were also coughing. It was just one of those things, and surely it would go away.

Except it didn’t. The cough lasted. It woke her up at night, it woke me up at night. Her younger sister took to sleeping in our room to avoid the hacking. We were all exhausted, but Olivia most of all. Thinking it might be her asthma, we chased her around with various inhalers, her pediatrician gave her steroids, and eventually we started her on an antibiotic. Nothing seemed to help. As I dragged Olivia into the doctor’s office after nearly three weeks of illness, I was at my wit’s end.

Amanda Naprawa and her 9-year-old daughter Olivia.

The author with her daughter Olivia, now nearly recovered from her bout of pertussis (whooping cough).

When her pediatrician suggested she be tested for pertussis (whooping cough), I almost laughed. Did this doctor not realize that I am the queen of vaccines? I love vaccines. Anything I can vaccinate against, count me in. So obviously there was no way that my daughter could have a vaccine-preventable disease like pertussis.

Except she did. Two days later, Olivia’s pertussis test came back positive. She had received all five recommended doses of the DTaP (diptheria, tetanus, & pertussis) vaccine, which is given to children between the ages of 2 months and 4 to 6 years. So how was it possible that she was infected?

About pertussis

Pertussis is a highly contagious bacterial infection that spreads from person to person by coughing, sneezing, or simply spending a lot of time with an infected person. For comparison, pertussis is second only to measles in terms of how readily it spreads, and it’s about six times as contagious as the flu. Just one infected person can spread pertussis to numerous other people, who in turn can infect numerous others.

Early symptoms of pertussis can be quite mild, such as a runny nose and mild cough. Within a week or two, however, classic symptoms may appear, including rapid coughs followed by a tell-tale high-pitched “whoop.” Not all infected people will develop a whoop; other symptoms include vomiting and exhaustion after prolonged coughing fits. While pertussis can be serious in children and adults, it’s especially dangerous and even potentially life-threatening in infants.

Antibiotics can reduce the severity of pertussis in people who are infected but haven’t yet started coughing; if the person has already developed symptoms, antibiotics may not help reduce them, but the drugs can still help cut the likelihood of passing the illness on to others (provided they’re started within the first three weeks of illness).

Why the pertussis vaccine isn’t foolproof

The best way to avoid pertussis is to be vaccinated. But as we learned in Olivia’s case, even vaccinated kids can become infected. Why? This happens for a few reasons:

First, although Olivia was vaccinated, the bacteria that cause pertussis are very much alive in the community, where they’re waiting for a person to infect. When a sufficient proportion of people in the community are vaccinated—for pertussis, the threshold is about 92 percent—the bacteria have a harder time finding someone to infect. This is known as herd immunity. Publicly available records show that about 95 percent of the students at my daughter’s school are immunized against pertussis. But that isn’t the case in all of the San Francisco Bay Area, where we live. At some private schools, in fact, a quick search revealed vaccination rates of less than half.

When the number of vaccinated people in a community dips below the threshold, herd immunity decreases and disease outbreaks become more likely. The more contagious the disease, the quicker you're likely to see an outbreak. Measles and pertussis are among the most contagious diseases, which is why their herd immunty threshold is relatively high—and why declining vaccination rates for those diseases have coincided with outbreaks of both in California and elsewhere.

Related: Vaccine Opt-Out Rates Rise

Another reason is that the pertussis vaccine, while effective and life-saving, is not perfect. Over time, the effectiveness of the vaccine decreases. This is known as “waning immunity.” In the case of the DTaP vaccine, about nine out of 10 kids are fully protected against pertussis in the two years after completing the recommended doses. But this drops to seven out of 10 kids five years after vaccination.

Adults and children over age 11 receive a different version of the vaccine (Tdap) that affords slightly less protection against pertussis than DTaP. After about four years, the CDC estimates that only three or 4 out of 10 adults remain fully protected. (This is why women are instructed to get a Tdap booster with each pregnancy, as are family members who will be in close contact with the newborn.) Olivia is now about five years out from her last dose of DTaP, putting her at just the unfortunate age to be losing vaccine protection. And she still has to wait another two years, until she’s 11, to get the Tdap shot.

Once we knew that Olivia’s cough was more serious than we’d thought, we were sure to let others, including her school, know too. In many instances, antibiotics may be prescribed to people who have been in close contact with a pertussis-infected individual (even if they are showing no signs of infection themselves), to prevent serious symptoms and to limit their ability to spread the disease if they do develop it. So, if you or your child ever tests positive for pertussis, let people who’ve been in close contact with the infected person know so that they can find out if they should be treated as well.

Bottom line: Yes, my child got a vaccine-preventable disease. But I am still the queen of vaccines. Please don’t let this story deter you from getting vaccinated. Just because the pertussis vaccine is not 100 percent effective, it is still very protective. If you do contract pertussis, vaccinated people typically have much less serious infections than unvaccinated people (I am pleased to say that Olivia is almost fully recovered). And when you vaccinate yourself and your kids, you are contributing to the herd immunity in your community, which protects all of us—including those, young and old, who aren’t able to be vaccinated, such as individuals with certain allergies or who are immune-compromised from disease or medications.

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For a full list of vaccine-related articles, see the Vaccines section of our website.