“The second generation of vaccine turned out to have an unanticipated limitation, and that has been probably the main engine driving the resurgence,” says Gill, who is lead author on a review article on the resurrection of whooping cough, published in the journal F1000 Research. Gill and his colleagues suspect that the vaccine, while preventing symptoms from pertussis infections for some time, has little impact on preventing people from becoming “colonized” with the bacteria, meaning they are asymptomatic carriers of the disease and are still capable of infecting others.