Almost twice as many parents in New York sought religious exemptions from vaccination in 2011 compared to 12 years earlier, and cases of whooping cough (pertussis) increased simultaneously, the study found.
Counties with exemption rates of 1 percent or more experienced higher rates of whooping cough in both unvaccinated and vaccinated children—33 cases per 100,000 children on average compared to 20 cases per 100,000 in counties with lower exemption rates, the study found.
Statewide, the rate of exemptions grew from 0.23 percent to 0.45 percent between 2000 and 2011, Shaw said, noting that the total number is still low.
"But some counties are much higher—up to 5.58 percent," said Shaw, whose results were released online June 3 in the journal Pediatrics.
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