Refusal to Vaccinate Linked to 2010 Pertussis Outbreak

The 2010 pertussis outbreak in California may have been related to parents’ refusal to vaccinate their school-aged children, according to a new study published in Pediatrics.

Researchers at Emory University led by Jessica E. Atwell, MPH, found that nonmedical exemptions (NMEs) from vaccination for children entering kindergarten appear to be one of several factors behind the resurgence of pertussis in California’s largest outbreak since 1947. According to the researchers, the overall rate of NMEs — which are also called personal belief exemptions — rose in California from 0.77 percent of all children entering kindergarten in 2000 to 2.33 percent in 2010.

The study found that more pertussis cases occurred within exemption clusters than outside of them, even after adjusting for demographic factors (incident rate ratios = 1.20; 95 percent confidence interval, 1.10-1.30).

Other possible causes of the 2010 pertussis outbreak include the hypothesis that the currently administered acellular vaccine is less effective than the older whole-cell vaccine. Even if the newer vaccine has the same initial efficacy as whole-cell vaccine, another theory is that its effectiveness may wane over time.