Whooping Cough Vaccine Wears Off Quickly, Researchers Say

New research suggests that the effectiveness of the vaccine for whooping cough wears off after three years, a finding that provides a possible explanation for a troubling outbreak of the respiratory infection in California last year.

As The Associated Press reports, the preliminary results of the research show that children who recently received the recommended series of vaccinations against the highly contagious disease were well-protected against whooping cough. By contrast, based on a small sampling of children in northern California, the risk of contracting whooping cough appeared to be as much as 20 times higher in children three years or more after vaccination.

That could help explain why significant numbers of children who were fully, but not recently, immunized have come down with whooping cough.

The new research, unveiled in a press briefing at a medical conference in Chicago Monday, indicated that “the vast majority” of those who became ill were fully vaccinated children, said Dr. David Witt, the lead researcher and chief of infectious disease at the Kaiser Permanente Medical Center in San Rafael, Calif.

“I was disturbed to find maybe we had a little more confidence in the vaccine than it might deserve,” Witt said.

His research looked at roughly 15,000 children in Marin County in in the San Francisco Bay Area. The sampling included 132 who contracted whooping cough, many of whom were in the 8-to-12 age range.

As Wired reports, Witt said the greatest concern is that the children who were presumed to be protected could be transmitting the infection to others in their families and neighborhoods who were vulnerable. Grandparents with weak immune systems and infants with undeveloped ones would be particularly at risk, he said.

The further problem, Witt said, is that the fading immunity in vaccinated children could add to the vulnerability created by families who refused to vaccinate their children or who vaccinated their children late.

In California last year, more than 9,100 people became ill and 10 babies died from the epidemic of whooping cough, also known as pertussis. In response, California schools have refused admission to thousands of middle and high school students this fall who haven’t received a booster shot.

Health care officials recommend that children receive five doses of the vaccine, beginning at two months and continuing until they reach between four and six years old. A booster shot is recommended when a child reaches age 11 or 12.

Officials at the federal Centers for Disease Control and Prevention acknowledged that the vaccine’s protection declines over time, but they said their own studies show the drop-off is not as pronounced as Witt’s research found. The agency says the pertussis immunizations — DTaP for children and Tdap for  adolescents and adults — remain the best means of prevention.

ROBERT T. NELSON

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