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Whooping cough shot cuts illness, maybe not spread

| Monday, Nov. 25, 2013, 4:51 p.m.

ATLANTA — A government study offers a new theory on why the whooping cough vaccine doesn't seem to be working as well as expected.

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 for whooping cough in six decades. Health officials received reports of more than 48,000 cases, including 18 deaths.

Some studies have concluded the newer vaccine doesn't last as long as the old one. But a study by Merkel and his colleagues offers a new wrinkle.

Their research used baboons, considered the most humanlike model for studying whooping cough. Baboons at ages 2, 4 and 6 months were vaccinated and then exposed to whooping cough at 7 months — when vaccine protection would be new and strong.

The baboons didn't get sick, but they had high levels of bacteria in their respiratory system for five weeks, which suggest they were contagious for about that long. Some baboons given the old vaccine had low levels after two weeks.

That's a big-deal finding because it 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.

The study was published Monday in the journal Proceedings of the National Academy of Sciences.

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