Health Information

Young children who are immunized against whooping cough (pertussis) are well protected against this illness, but a new study finds that the vaccine's effectiveness declines sharply after just three years.

David Witt, M.D., at Kaiser Permanente Medical Center in San Rafael, Calif., and his colleagues sifted through the medical records of about 15,000 children in an attempt to figure out why that region was experiencing an outbreak of pertussis.

They found 171 confirmed cases of pertussis between March and October 2010. Of that number, 103 were in children ages 12 or younger. On closer examination, Dr. Witt determined that the number of pertussis cases "skyrocketed" once children reached age 8.

Middle schoolers

Preteens seem to be at highest risk for contracting pertussis, he says. Infants and preschoolers who are up to date on their pertussis vaccinations are protected against the disease, but as children move into later childhood, their immunity seems to wane. In fact, the rate of infection was the same in the 8- to 12-year-old age group for children who had been immunized and those who had not.

Dr. Witt says the number of pertussis cases dropped off again as children got their booster shot at age 12.

Infants at risk

Although many of the preteens who fell ill had only a mild case of the disease, the real threat in a pertussis outbreak is the transmission to other family members, especially infants. Infants younger than 6 months have not yet received their third dose of the vaccine and so are more vulnerable to the infection.

Dr. Witt, who presented his findings at a recent conference of the American Society for Microbiology, isn't recommending that the pertussis booster be given earlier than age 12. Although he and his colleagues did do so successfully during last year's outbreak, more research is needed to confirm his findings.

Always talk with your health care provider to find out more information.