The study suggests that the new whooping cough strain is resistant to Pertactin, a component of the acellular vaccines. This resistance may be why we are seeing increase in the number of people getting the disease.
Original source:
Pertactin-Negative Variants of Bordetella pertussis in the United States - NEJM
http://www.nejm.org/doi/full/10.1056/NEJMc1209369
