We've reported on the evolution of whooping cough before. Researchers have found evolved pertussis, as whooping cough is scientifically known, in Finland, France, Italy, Japan and the U.S. As we previously reported, the evolved bacteria don't seem to be more dangerous than their predecessors. Nevertheless, the U.S. Centers for Disease Control and Prevention are keeping an eye on whooping cough's evolution. It could help explain another recent pertussis phenomenon: The newest pertussis vaccines seem to wear off much faster than older ones, leaving kids vulnerable at age 8 or 10 unless they get booster shots.

In Australia, researchers from several universities and hospitals examined samples of pertussis dating back to 1997. What they saw happening there mirrored what's happened in the U.S.

In every country where scientists have found evolved pertussis, the bacteria don't make a protein called pertactin. Pertactin is thought to help un-evolved pertussis bacteria stick to the cells lining people's respiratory tracts. Scientists still have a lot to learn about pertactin, however. "There's still some speculation about that, how it functions in that role," CDC scientist Lucia Pawloski toldPopular Science in December.