Archive for September 17th, 2012

The problem of waning pertussis immunity

There’s been a lot of discussion, both in the scientific literature and online, about recent pertussis outbreaks, which are the worst outbreaks in the US in the last 50 years. How could this possibly be, it is asked, when vaccine uptake for the pertussis vaccine remains high? True, there are pockets of vaccine resistance, where uptake of the vaccine is low, but it’s becoming increasingly clear that, unlike the case of measles outbreaks, low uptake of the pertussis vaccine does not appear to be nearly enough to explain the frequency and magnitude of the outbreaks. Given that it’s been a while since any of us has discussed the recent pertussis outbreak here on SBM, I thought that it would be a good time for me to do so, particularly because there have been some new studies and new developments since April, including a paper hot off the presses last Thursday in the New England Journal of Medicine. As a result, those of you who read me at my not-so-super-secret other blogging location might find some of the material in this post familiar, but given the new NEJM paper, I thought that now would be a good time to synthesize and update what I’ve discussed before in different forums in a more comprehensive way, even at the risk of some repetition of previous material I’ve published elsewhere. Hopefully, it will also provide materials for skeptics and supporters of SBM to counter the antivaccine movement, which has pounced on the recent pertussis outbreaks as evidence that the “vaccine doesn’t work.”

Without a doubt (to me, at least), the biggest difference between science-based doctors and quacks is a very simple one. When a treatment or preventative measure isn’t working as well as it should, we science-based physicians ask why. We try to find out what is not working optimally and why. Then we try to figure out how to make things better. So it is with the acellular pertussis vaccine. This vaccine protects against whooping cough, which is caused by Bordetella pertussis, and is administered to children in the form of a combination vaccine, the DTaP (diptheria/tetanus/acellular pertussis). Five doses are recommended for children, the first at age 2 months, and then at ages 4 months, 6 months, 15-18 months, and 4-6 years. There is also the newer formulation, the Tdap (tetanus, diptheria, and acellular pertussis), which is recommended for people between the ages of 11 and 64. The Tdap is now usually administered first at age 11-12, with additional recommendations for a Tdap booster in adolescents and adults summarized here, here, and here. Unfortunately, although the vaccine works, recent outbreaks have suggested that we need to change our approach to pertussis vaccination. Let’s see why.

Posted in: Vaccines

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