What would actually happen if only 80 percent of school-age children were vaccinated against the measles? It's a scary thought that a new simulation from the University of Pittsburgh aims to visualize.

On the Framework for Reconstructing Epidemiological Dynamics, or FRED for short, users can select a state and a city to see how two very different scenarios would play out over 238 days. The first example from FRED, below, shows what would happen in Manhattan if 80 percent of school-age children were vaccinated. The second example shows the result if the borough had 95 percent vaccination coverage.

The first map shows a devastating outbreak because the city has lost its herd immunity, which occurs when too few people are vaccinated to protect the community. On the second map a few measles cases pop up, but the population ultimately stays protected because enough people are vaccinated.

Unfortunately, the average vaccination coverage for one-year-olds across the U.S. was 91 percent in 2013. In 10 states--Arkansas, Colorado, Idaho, Iowa, Kansas, Maine, North Dakota, Pennsylvania, Vermont and Washington--coverage for children in kindergarten was below 92 percent during the 2013-14 school year, according to the U.S. Centers for Disease Control and Prevention.

One of the drivers behind the current measles outbreaks is the increasing number of parents seeking vaccine exemptions for their children. From the beginning of this year through Feb. 27, 170 cases were reported to the CDC, largely stemming from the outbreak at Disneyland. Last year had the highest number of reported cases (644) since 2000. During the 2013-14 school year, 10 states had more than 4 percent of kindergartners with vaccine exemptions (Alaska, Arizona, Colorado, Idaho, Maine, Michigan, Oregon, Utah, Vermont and Wisconsin). The map below shows vaccination coverage and exemptions by state.

Explore simulations of other cities experiencing measles outbreaks on FRED here (it works best in Google Chrome and Safari browsers).