“According to the Washington Post:3

“‘[I]t was thought that people only spread the disease when they had coughs and other symptoms,’ said Dr. Erik Hewlett, a University of Virginia whooping cough researcher who was not involved in the FDA study but has collaborated with Merkel.

Health officials have sought to protect small children by vaccinating the people who are in contact with them such as grandparents and baby sitters— a strategy called ‘cocooning.’ But that may not work as well as hoped if infected people who don’t show any symptoms can still spread it, the research suggests. ‘This is a whole new way of thinking of the problem,’ Hewlett said.””

Read more: http://articles.mercola.com/sites/articles/archive/2013/12/10/whooping-cough-pertussis-vaccine.aspx