Not good: This year there will be the most cases of whooping cough in more than a half century.
The CDC is trying to figure out what’s going on, but Schuchat said a couple of factors are clearly at work. The formulation for the whooping cough vaccine was changed in 1997, and kids hitting age 13 and 14 now are the first to have been fully vaccinated with five doses of the new vaccine. The new formulation causes less of a reaction, but it may also wear off sooner, Schuchat said.
The older vaccine was made using a whole pertussis bacterium. It was very effective, but it did cause swelling in some kids who got it, and sometimes caused a fever — something that scared parents. It also was widely blamed for causing rare but serious neurological reactions, although Schuchat said studies have not confirmed this.
I imagine the formulation was changed because of the uproar in the 1990s about the dangers of the old vaccine.