Today, the measles vaccination rate is above 95 percent for children of kindergarten age. But there has been a small but growing trend of parents seeking exemptions for their children from school-entry vaccination requirements for religious or philosophical reasons. Other parents have tried to space out, or delay, measles vaccinations because of fears that the shot will trigger autism or other problems.
Measles outbreaks are more common in communities where such beliefs are more common, experts say. "It's often concentrated there. Folks who think similarly tend to live in the same neighborhood or attend the same religious organization," Schaffner said.
The CDC national tally may already be outdated. Also on Thursday, Ohio officials announced a new cluster of 13 suspected cases in rural Knox County. At least three traveled to the Philippines last month on a religious humanitarian mission.
About 17 percent of U.S. cases this year were vaccinated. Health officials say that although the vaccine is very effective, it's not perfect.
CDC report: http://www.cdc.gov/foodsafety/