“The current increase in measles cases is being driven by unvaccinated people, primarily U.S. residents, who got measles in other countries, brought the virus back to the United States and spread to others in communities where many people are not vaccinated,” said Dr. Anne Schuchat, assistant surgeon general and director of CDC’s National Center for Immunizations and Respiratory Diseases. “Many of the clusters in the U.S. began following travel to the Philippines where a large outbreak has been occurring since October 2013.”

Of the 288 cases, 280 (97 percent) were associated with importations from at least 18 countries. More than one in seven cases has led to hospitalization. Ninety percent of all measles cases in the United States were in people who were not vaccinated or whose vaccination status was unknown. Among the U.S. residents who were not vaccinated, 85 percent were religious, philosophical or personal reasons.