Refusal to receive vaccination is associated with an increased risk for measles and pertussis, according to a report published in JAMA. 

Lead author Varun K. Phadke, MD, and fellow investigators analyzed published reports of measles outbreaks that have occurred since January 1, 2000, when the United States declared that measles had been eliminated; reports of endemic and epidemic pertussis since January 1, 1977, the lowest point in incidence in the United States; and for studies on disease risk in the context of vaccine delay or exemption. 

They included 18 published studies that described 1,416 measles cases (patient age, 2 weeks-84 years); 56.8% of the patients had never been vaccinated against measles. Of the 970 measles cases with detailed vaccination data, 574 were eligible for the vaccine but chose not to receive it, and 405 (70.6%) of these had nonmedical exemptions. The researchers identified 32 reports of pertussis outbreaks, which included 10,609 individuals (age, 10 days-87 years) with a vaccination status included.

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They found that in the 5 largest statewide epidemics, 24% to 45% of those affected were unvaccinated or undervaccinated, but several outbreaks occurred in highly vaccinated populations, suggesting waning immunity instead, the authors said.