Pertussis Vaccine Fades Over Time

Rates of whooping cough (pertussis) have increased in recent years. One concern has been that the vaccine for pertussis becomes weaker over time. A recent study found this to be the case. During a California outbreak of pertussis, many of the grade school children had received their DTaP vaccine for pertussis.

However, researchers found that children were more likely to get pertussis the longer it had been since their last pertussis booster shot. The vaccine's effectiveness had declined over time since their fifth (final) shot.

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The study was led by Lara K. Misegades, PhD, MS, of the Epidemic Intelligence Service and Meningitis and Vaccine Preventable Diseases Branch at the National Center for Immunization and Respiratory Diseases.

Dr. Misegades and her colleagues looked at 682 cases of pertussis among 4- to 10-year-olds within 15 California counties in 2010. They compared the immunization rates of these children and the time since their last pertussis shot to those of 2,016 children in the same counties who did not get pertussis. They found that 53 of the children who got pertussis (7.8 percent) had not received any vaccinations for pertussis, compared to 19 of the children who did not get pertussis (0.9 percent).

Overall, the children who contracted pertussis were far less likely to have received all five doses of the pertussis vaccine.

Among those who did receive all five doses and still had pertussis, however, these children were less likely to have gotten their fifth booster shot within the past year. The researchers found that this pattern continued when they looked at how much time had passed since the fifth booster shot among the other vaccinated children with pertussis.

In general, the more time that had passed since the child had gotten their last pertussis booster shot, the more likely it was that they had contracted pertussis.

Therefore, the effectiveness of the vaccine declined with each year since the child had received his or her fifth and final dose of the DTaP vaccine.

The study was published November 27 in the journal JAMA. The research did not receive external funding, and the authors declared no conflicts of interest.