Vaccines for whooping cough contain three to five protective antigens, the presence of which are critical to the vaccine's effectiveness. But one of the antigens, pertactin, which had been present in almost all isolates of Bordetella pertussis in the US as late as 2010, is now absent from more than half of them, according to a paper published ahead of print in Clinical and Vaccine Immunology. "These findings tell us that there is an evolutionary advantage to lacking the protein that may have important vaccine implications," says first author Lucia C. Pawloski, of the Centers for Disease Control and Prevention, Atlanta, GA.