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Questions and Answers About Pertussis (Whooping Cough) with Sean O’Leary, MD

In light of the recent pertussis (whooping cough) epidemic occurring in Colorado, we asked Dr. Sean O’Leary, a pediatrician and pediatric infectious diseases specialist at Children’s Hospital Colorado, to answer your most commonly asked questions about pertussis. Read on to learn how you can keep your family healthy and protected.

What’s going on with Whooping Cough? I’ve been hearing about outbreaks in the news. Why are we seeing an increase in cases? Why do some people who are immunized still get it?

These are important but complicated questions, and there are several factors contributing to the rise in pertussis (whooping cough). It’s not really clear how much each separate factor is contributing to the problem, but I will attempt to answer this with the latest information available.

Pertussis, also known as whooping cough, is caused by a bacteria called Bordatella pertussis. It often starts out as a mild cold, but can progress to severe cough, difficulty breathing, and death. In older children and adults, it may cause just a cold-like illness or it may cause a prolonged severe cough (the Chinese translation is the “hundred day cough”). It is most severe in young infants and un-immunized and under-immunized children. Worldwide there are still about 300,000 deaths per year from pertussis. In the US, the rate of pertussis has been steadily increasing since the mid-70s. While the reasons for this rise aren’t entirely clear, I’ll outline the likely contributing factors, in no particularly order.

1. We have better tools for diagnosing pertussis and more providers are aware of the epidemic, so at least part of the rise may be explained by more people testing for the illness and more positive tests in those who have it. Because more providers are now aware that there is an epidemic of pertussis going on, they are more likely to test a patient who has had a cough for a few weeks than they were 10 or even 5 years ago. In other words, at least some of the increase isn’t really an increase – it’s just that now we know about it when before we didn’t.

2. Waning immunity means that the further a person is out from their initial vaccine (or infection), the less immune they are to the disease. For pertussis, we know that neither infection nor immunization provide lifelong immunity. However, when someone who has been immunized (or who has had actual pertussis) gets pertussis, the illness may not be as severe. For example, a teenager who received all the doses as a child (but not a recent booster) may contract pertussis at school. All this teen may get is a cough not much different than the common cold because they have some immunity. However, they are still contagious with pertussis and could pass it on further at school or to their unprotected infant sibling, who then goes on to develop a severe case.

3. Further complicating the waning immunity issue is that there have been 2 main vaccines for immunization against pertussis used in the US: DTP, and DTaP. They look very similar in name but there are important differences. DTP was used until the mid-1990s in the US, and is also called the whole cell pertussis vaccine. What this basically means is that the bacteria was killed and then ground up to make the vaccine. That vaccine contains about 3000 antigens – or proteins – that stimulate an immune response. The DTaP vaccine, also called the acellular pertussis vaccine, contains just 3-5 proteins from the bacteria. The reason the DTaP vaccine was developed and adopted was because the old whole cell DTP vaccine caused lots of reactions such as fever, inconsolable crying for a few hours, and soreness at the site of injection. It was also thought at the time that very rarely (1 in millions) it could cause much more severe reactions. In retrospect, as more sophisticated genetic testing has become available, it appears that many of the children thought to have been harmed by the whole cell DTP vaccine actually had genetic conditions unrelated to the vaccinations. The reason all of that is important is that it is becoming clear that the newer DTaP vaccine currently in use does not protect people as long as the old vaccine, so children and adolescents who got DTaP vaccine are more likely to contract and spread pertussis than those who got the old DTP vaccine.

4. Recognizing the need to boost immunity to pertussis, a newer vaccine came out called Tdap, for use in older children, teens, and adults. It is effective at boosting immunity to pertussis, but there are many teens and even more adults who have not received this booster, leaving them essentially unprotected.

5. Parents refusing vaccines and ‘spacing out’ vaccines also play a role in the current epidemic. Even though the DTaP vaccine may not be as protective as the old one, it is clearly much better than not getting vaccinated. Anti-vaccine advocates often use mathematical sleight of hand to make parents think it is better not to get vaccinated by promoting this fact: in total numbers more children who get pertussis have been vaccinated than those who haven’t been vaccinated. This is because >95% of children in the US have been vaccinated against pertussis, far outnumbering the unvaccinated. Because no vaccine is perfect, some children who are immunized will still develop pertussis if exposed. An example: Let’s say there are 10,000 vaccinated children and 500 unvaccinated children in a community and they are all exposed to pertussis because of a major outbreak. If the vaccine is 80% effective, 20%, or 2,000, of the vaccinated children will get the illness but 100%, or all 500, of the unvaccinated children will. Yes, 2000 is greater than 500, but there are 8,000 vaccinated children who didn’t get the disease. Also keep in mind that the disease tends to be less severe in those who get pertussis but have been previously immunized.

6. Finally, pertussis epidemics historically have occurred in cycles of 2-5 years, so we are likely in the midst of one of those. Still, though, the national incidence of pertussis is less than 1/20th of what it was in the 1930s, the pre-vaccine era.

The most important thing we can do right now is encourage everyone to be up-to-date on pertussis vaccinations, particularly those who have close contact with young infants. It is these young infants that are at highest risk of severe disease and death from contracting pertussis.

SeanOLearyMDDr. O’Leary is a pediatrician and pediatric infectious diseases specialist at Children’s Hospital Colorado. Prior to working at Children’s Colorado, he was a general pediatrician in a busy private practice for 8 years. In that time, he encountered many parents with concerns about vaccines. We asked Dr. O’Leary to talk a little about his experiences with parents who have questions about vaccines: “Initially, I was concerned that these parents did not trust my judgment when I recommended vaccines for their children. I came to realize, though, that asking about vaccines was no different than any other part of parenting. These parents weren’t questioning my judgment: they just wanted to do what’s best for their children, and there is a lot of conflicting information about vaccines out there. Wanting to do more to help parents better understand vaccines was one of the main reasons I decided to return to Children’s Hospital Colorado and become a researcher and educator. I now spend much of time attempting to do just that: talking with other physicians about the best ways of communicating with families about vaccines, doing vaccine related research, and yes, still talking with families about vaccines.” On a personal note, Dr. O’Leary is married and has two children, six chickens, and a very old dog.

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