Compared to other types of vaccines, measles vaccination is quite popular. Roughly 93 percent of children are properly vaccinated against the infectious virus. But fueled by the anti-vaccination movement in the U.S., pockets of unvaccinated children have been growing in recent years. What's more, the measles virus is so contagious that even 92 percent isn't high enough to prevent outbreaks.
Researchers say the communities that spawned the latest outbreak, as well as those that were exposed to and spread the outbreak, were likely vaccinated at substandard rates.