After 50 years of mass immunisation, cases of whooping cough (pertussis) continue to rise. But why? It's because the vaccine actually encourages the growth of one of the bacterium responsible for the disease, researchers have discovered.
Whooping cough is caused by one of two forms of bacterium: the more common Bordetella pertussis-which the vaccine deals with successfully-and Bordetella parapertussis.
Not only are the antigens in the vaccine designed to exclusively eliminate the B.pertusiss bacteria, they create an environment that actively encourages and makes more potent the B.parapertussis bacteria.
Researchers from Sheffield University made the discovery when they measured the effectiveness of the acellular whooping cough vaccine against the two bacteria; although it cleared the B.pertussis bacterium, there was a 40-fold increase in the B.parapertussis bacterium in the lungs. The vaccine also blocks the body's own immune system from fighting the bacterium.
(Source: Proc Biol Sci, 2010; 277 (1690): 2017-25).