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Students leave the school nurse office after receiving a vaccine against whooping cough before giving it to students at Mark Twain Middle School August 7, 2012 in Los Angeles, California. The boosters, also called Tdap shots, are required of all seventh graders before they can start school.
Whooping cough was once a disease which killed thousands of children every year. When a vaccine was introduced in the 1940s, and rates dropped significantly, but then about three years ago an outbreak of the disease hit California.
New research sheds light on what happened. For more on this we turn to Dr. James Cherry, a Pediatric Infectious Disease doctor at UCLA's medical school.