Study: Whooping cough vaccine loses punch

As the United States 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 yesterday'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.

There have been more than 26,000 U.S. 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.

In light of the findings and earlier, similar research, health officials are considering recommending another booster shot, strengthening the vaccine or devising a new one.

Whooping cough, or pertussis, is a highly contagious bacterial disease that can strike people of any age but is most dangerous to children. -- AP