Pertussis outbreak strikes hard at infants, teens

Infants have borne the brunt of the worst outbreak of pertussis, or whooping cough, in almost 70 years in California, the Centers for Disease Control and Prevention (CDC) reports. Large numbers of older children and teenagers are also affected.

Between January 1 and November 26 of this year, 9935 cases of pertussis-or 26 per 100,000 population-were reported in California. Infants aged younger than 1 year had the highest incidence, 174.6 cases per 100,000. Adolescents aged 15 years had the next highest incidence, 137.8 cases per 100,000. Overall, the greatest incidence aside from infants occurred in young persons aged 14 to 16 years. In June, the California Department of Public Health declared a pertussis epidemic in the state.

Infants aged younger than 1 year, who are most likely to suffer severe complications and die from pertussis, accounted for 275 of the 347 hospitalizations for the disease. Of the hospitalized infants, 214 were aged younger than 4 months. One death was reported, a 5-week-old infant (2 other infants, who had contracted pertussis in 2013, also died).

Only 17% of mothers of infants who came down with pertussis during this year’s outbreak had been vaccinated during pregnancy, as recommended by the CDC’s Advisory Committee for Immunization Practices (ACIP). The ACIP recommends that pregnant women receive a tetanus-diphtheria-acellular pertussis (Tdap) booster during the third trimester to protect babies until they can begin immunization at 2 months of age. Recent research has found that vaccinated pregnant women pass antibodies to the fetus through the placenta.

“Strategies to prevent the most severe cases of pertussis, which occur primarily in young infants, should be prioritized,” the CDC emphasizes.

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Among adolescents who contracted pertussis, only 2.2% had never received pertussis vaccine, and 87% had received Tdap at least 3 years previously, probably indicating waning immunity. The effect of acellular pertussis vaccines wanes more quickly than earlier whole-cell vaccines. “It is likely that increased incidence will continue to be observed among this cohort [teenagers] in the absence of a new vaccine or more effective vaccination strategy,” the CDC report notes. 

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