The resurgence of vaccine-preventable diseases in the United States prompted researchers to examine the association between vaccine refusal and the epidemiology of diseases such as measles and pertussis. The findings of the study were published in JAMA.
The study includes an analysis of 18 published measles studies and 32 reports of pertussis outbreaks. Highlighted below are six findings from their analysis.
1. Of the 1,416 measles cases included in the published studies, more than half (56.8 percent) had no history of measles vaccination.
2. The studies included 970 measles cases with detailed vaccination data. Of those, 574 cases were unvaccinated despite being vaccine eligible.
3. Nearly three-quarters (70.6 percent) of the unvaccinated cases were based on nonmedical exemptions, including religious or philosophical reasons, and 41.8 percent were based on medical contraindications. Patients could pick more than one reason to refuse a measles vaccine.
4. Among the 10,609 individuals whose vaccination status was included in the pertussis reports, unvaccinated or undervaccinated individuals made up between 24 and 45 percent of the cases included in the five largest statewide epidemics.
5. That said, pertussis broke out in several highly vaccinated populations as well, indicating waning immunity.
6. Nine reports (covering 12 outbreaks) provided detailed vaccination data on unimmunized cases. Eight pertussis outbreaks included in the reports occurred in places where intentionally unvaccinated individuals made up 59 to 93 percent of all unvaccinated individuals.
"A substantial proportion of the U.S. measles cases in the era after elimination were intentionally unvaccinated. The phenomenon of vaccine refusal was associated with an increased risk for measles among people who refuse vaccines and among fully vaccinated individuals," concluded the study. "Although pertussis resurgence has been attributed to waning immunity and other factors, vaccine refusal was still associated with an increased risk for pertussis in some populations."
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