Last year, the United States suffered more than 1,200 cases of measles — the largest measles outbreak in 20 years. The reason, not surprisingly, was that a critical number of parents — often in pockets like Clark Country, Washington, and Brooklyn, New York — had chosen not to vaccinate their children.

To forecast the expected size of measles outbreaks looking forward, researchers from Pittsburgh and Texas examined the expected size of outbreaks in relation to the percentage of unvaccinated children (Sinclair D, et al. Forecasted Size of Measles Outbreaks Associated with Vaccination Exemptions for Schoolchildren. JAMA Network Open. 2019 Aug 2;2(8):e199768. doi:10.1001/jamanetworkopen.2019.9768). Using a decision analytical model of areas in Texas, they simulated 1,000 outbreaks based on various levels of vaccine exemptions. They found that 1 in 20 simulated measles outbreaks would involve more than 400 cases in the Austin and Dallas, Texas, metropolitan areas. About 64% of those cases would occur in children for whom a vaccine had been refused and 36% in bystanders.

The authors concluded, “This study suggests that vaccination rates in some Texas schools are currently low enough to allow large measles outbreaks.”

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