Whooping Cough Vaccine Less Effective Than Hoped; Researchers May Know Why

The research suggests that while the vaccine may keep people from getting sick, it doesn't prevent them from spreading whooping cough — also known as pertussis — to others.

"It could explain the increase in pertussis that we're seeing in the U.S.," said one of the researchers, Tod Merkel of the Food and Drug Administration.

Whooping cough is a highly contagious disease that can strike people of any age but is most dangerous to children. It was once common, causing hundreds of thousands of illnesses annually and thousands of deaths. But after a vaccine was introduced in the 1940s, cases dropped to fewer than 5,000 a year.

The vaccine was replaced in the 1990s because of side effects that included pain and swelling from the shot and fever. The newer vaccine is part of routine childhood vaccinations as well as adult booster shots.

But cases have rebounded. Last year was the nation's worst year for whooping cough in six decades — U.S. health officials received reports of more than 48,000 cases, including 18 deaths.

This year hasn't been half as bad — about 20,000 reported illnesses, including six deaths so far. Whooping cough ebbs and flows in cycles, so experts aren't surprised to see cases recede. But 20,000 can still be seen as a lot when a widely used vaccine is supposed to protect the public.