Last time I wrote about Whooping Cough (Pertussis) was in the Summer of 2010, right in the middle of a big outbreak in California. It turns out that a group did a big study using that very outbreak to look at the Whooping Cough vaccine and its effectiveness. The study expected to find that the outbreak would be common among unvaccinated children and not among those that had been vaccinated. And it did sort of. The unvaccinated group was indeed affected and caught the disease at a higher rate. But one group of vaccinated kids also caught the disease at a high rate – children aged between 8 and 12. These children were all in the gap between booster shots of the vaccine.
The data implies strongly that the vaccine is not as effective for as long as was previously thought. It has long been known that the Pertussis vaccine fades and needs a booster but it was thought to be effective for five years. The new study shows it to be effective for 2 to 3 years. So more frequent boosters are going to be needed. The study does, however, confirm that the vaccine is effective and also that even as the vaccine wears off, it still provides some residual protection. That residual protection can be important since whooping cough can be fatal, especially in young infants.
The last time I wrote I gave five strange but true facts about Pertussis. These are all still valid and worth knowing, but one of them is now wrong – the first one says that the vaccine loses effectiveness over time and that part is true, but it says that it lasts five years. For five years you should now read two-and-a-half.