Children who did not get vaccinated against whooping cough contributed to the 2010 outbreak of the illness, when more cases were reported than in any year since 1947, researchers said.
Researchers who looked at the geography of the cases suggest that clusters of “nonmedical exemptions” to immunizations were one of several factors in the California outbreak. They reported their findings on Monday in the journal Pediatrics.
In California in 2010, there were 9,120 cases of the illness known as pertussis — one-third of the U.S. cases. Los Angeles had 1,000 of those cases. Whooping cough is a respiratory ailment marked by bouts of coughing that are accompanied by a noise that can frighten parents — hence the name.
An earlier study published in the New England Journal of Medicine suggests that the DTaP (diphtheria, tetanus and pertussis) vaccine loses some effectiveness after the fifth of the five recommended doses. That, too, was part of the reason for the outbreak, the Pediatrics scientists said. They list the cyclical nature of pertussis and improved diagnosis as reasons for the high numbers.
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