If you live in California, chances are you remember the pertussis outbreak of 2010. That year, Los Angeles alone saw nearly 1,000 cases of the illness, also known as whooping cough, and the state as a whole saw around 9,000. This year, the nation is on pace to have its largest whooping cough caseload since 1959.
Now a new study suggests a troubling reason why such outbreaks may be becoming more common: The DTaP vaccine appears to wane in effectiveness after the fifth and final recommended dose, which is generally received around the age of 5.
Whooping cough, caused by a bacterium, can be a nasty respiratory illness that causes bouts of coughing and its namesake whooping noise, which is made by sufferers when they take deep breaths after a series of coughs.
In the new study, published this week in the New England Journal of Medicine, researchers at the Kaiser Permanente Vaccine Study Center in Oakland analyzed data from 277 children who tested positive for pertussis between 2006 and 2011, and compared them with over 3,000 children who tested negative, as well as an additional 6,000 matched controls.