Health News

Sep 13, 2012 10:47 AM by Lauren Molenburg

Whooping cough vaccine loses punch too fast

NEW YORK (AP) -- As the U.S. wrestles with its biggest whooping cough outbreak in decades, researchers appear to have zeroed in on the main cause: The safer vaccine that was introduced in the 1990s loses effectiveness much faster than previously thought.

A study published in Wednesday's New England Journal of Medicine found that the protective effect weakens dramatically soon after a youngster gets the last of the five recommended shots around age 6.

The protection rate falls from about 95 percent to 71 percent within five years, said researchers at the Kaiser Permanente Vaccine Research Center in Oakland, Calif.

The U.S. has had more than 26,000 whooping cough cases so far this year, including more than 10,000 in children ages 7 to 10.

"The substantial majority of the cases are explained by this waning immunity," said Dr. William Schaffner, an infectious-disease specialist at Vanderbilt University.

Whooping cough, or pertussis, is a highly contagious bacterial disease that can strike people of any age but is most dangerous to children. Its name comes from the sound youngsters make as they gasp for breath.

It used to be common, causing hundreds of thousands of illnesses annually and thousands of deaths. Cases dropped after a vaccine was introduced in the 1940s, and for decades, fewer than 5,000 a year were reported in the U.S.

Because of side effects that included pain and swelling at the injection site, fever and apparently, in rare cases, brain damage, the vaccine was replaced in the 1990s. The newer version used only parts of the bacterium instead of the whole thing and carried fewer complications.

But cases of whooping cough began to climb, sometimes topping 25,000 a year during the past decade. Also disturbing: The proportion of cases involving children ages 7 to 10 - most of them vaccinated - rose from less than 10 percent before 2006 to nearly 40 percent this year, according to the CDC.

The researchers found that the risk of getting whooping cough increases by about 42 percent a year after a child's last dose of vaccine.

The shortcomings in the vaccine did not become apparent until recently, when researchers had the benefit of several years of data uncorrupted by youngsters who received the old version.

Health officials have long recommended that children get vaccinated in five doses, with the first shot at 2 months and the final one between 4 and 6 years, and receive a booster shot at 11 or 12.

Now there's a growing consensus that something more needs to be done. Ideas include somehow pumping up the effectiveness of the vaccine or developing a new one. French scientists have been working on an experimental nasal spray vaccine.

Other ideas include administering the booster earlier than age 11 or adding another booster.

(Copyright 2012 The Associated Press. All rights reserved.)

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