Monday, March 27, 2017

The acellular pertussis vaccine, the legacy of fear

An infographic I made on the acellular pertussis vaccine

Note: I've decided to go back and post some of my older TMV Facebook page posts as blog posts to preserve them and make them more accessible. I decided to start with the post I made for my infographic on the acellular pertussis vaccine and how we got to that point.
Today's post is a bit different, but I would ask you read my entire post before reaching a conclusion about what I'm saying. Part of being a scientist is following the data no matter where it leads and how uncomfortable it is. With that, I present the case of the acellular pertussis vaccine and how we got to the point we are at now questioning the effectiveness of the vaccine. However, as I point out below, scientists are not the ones responsible for this vaccine that is far less effective at preventing asymptomatic infections, we have the anti-vaccine movement to thank for that. 

The acellular pertussis vaccine has been under heavy scrutiny the last few years and for good reason. Although it is a very safe vaccine, it just isn't nearly as effective as the older whole cell version of the vaccine. There have been several studies questioning the effectiveness of the acellular pertussis vaccine in preventing asymptomatic transmission, including the infamous baboon study that still found that the acellular vaccine provided robust protection against all but asymptomatic infections. New research strongly points to the acellular vaccine preventing serious infection and illness but not in preventing asymptomatic infections. This was the conclusion of a study that found that the genetic variation of pertussis was too great if it was being limited by the vaccine. Coupled with several other reviews, including a Cochrane Review, of how effective the vaccine is at preventing serious and mild cases of pertussis, it appears that asymptomatic infections may indeed be happening in the vaccinated populations. However, intentionally unvaccinated populations are still at a higher risk of pertussis than the vaccinated population.  

But how did we get to this point? By all measures, the whole cell pertussis vaccine is highly effective and offers superior protection compared to the acellular vaccine. Why would we abandon it for an inferior vaccine? It turns out that fear and the birth of the modern anti-vaccine movement caused this. Back in the early 1980s, a television news channel released an "expose" of the whole cell pertussis vaccine and inflated the risks of febrile seizures due to the vaccine. In actuality, the risk of febrile seizures is quite low at 6-8 out of 100,000 kids vaccinated, with risk of the seizures only on the day of the vaccination. However, parents and lawmakers demanded a safer vaccine and as a result the acellular pertussis vaccine was created and released in the early 1990s. It was deemed a success at the time as it is incredibly safe. 

But we sacrificed effectiveness for safety. Even as early as 1999, researchers began questioning the effectiveness of the acellular vaccine compared to the whole cell version. The latest research is the final nail in the coffin as it were for the acellular pertussis vaccine. Does this mean we should scrap the idea of a pertussis vaccine? Of course not. But we need to use science to improve the whole cell vaccine and maybe identify the component (or components) of the whole cell vaccine that induces lasting immunity so that we can generate a safe and effective vaccine.

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