The recommended percentage of people that should be vaccinated in a population of +250,000 to avoid a measles outbreak is 95 percent. A study was done to see what would actually happen if only 80 percent of children that are school-age were vaccinated against measles virus. The simulation showed a devastating outbreak in New York County; by day 238, over 75% of the county had been infected due to the fact that with only 80% of the population having been inoculated, the city had lost its herd immunity.
The average vaccination coverage for one year olds across the United States was only 91% in 2013. 10 specific states had lower than average coverage: Arkansas, Colorado, Idaho, Kansas, Iowa, North Dakota, Maine, Vermont, Pennsylvania, and Washington. The drivers behind the current outbreaks include a rising number of parents who seek vaccine exemptions for their children. In the first two months of 2015, over 170 cases of measles have been reported to the Center for Disease Control and Prevention. 2014 saw 644 reported cases, the highest number since 2000.
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