Even though measles was eliminated from the U.S.—meaning the disease no longer circulated on its own within U.S. borders—16 years ago, outbreaks have continued to result from occasionally imported cases. But the disease can only spread if enough people are not vaccinated against it—and that’s precisely why the U.S. has seen an increase in measles outbreaks. In fact, well over half of people who have caught measles in the past decade and a half were unvaccinated, and most of them had refused the measles vaccine, found a recent study in JAMA.
The numbers were not so dramatic for under-vaccination of pertussis in communities, however, because several other factors besides low immunization rates contribute to pertussis outbreaks, the authors explained.
“The phenomenon of vaccine refusal was associated with an increased risk for measles among people who refuse vaccines and among fully vaccinated individuals,” wrote Varun K. Phadke, MD, and fellow researchers at Emory University. “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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