The CDC has confirmed 387 cases across 15 states from Jan. 1 through March 28, compared with 372 cases in all of last year. There are now six outbreaks, defined as three or more cases, across four states: New York, Washington, New Jersey and California, according to the CDC. Measles is highly contagious, infecting up to 90 percent of unvaccinated people who are exposed to it. Measles can be especially dangerous for young children, the CDC says. It can lead to pneumonia, brain swelling and even death. The CDC recommends children get their first dose of MMR vaccine at between 12 and 15 months old and a second dose when they’re between 4 and 6 years old.

The MMR vaccine, which protects against measles, mumps and rubella, is the best way to protect against measles. Two doses, the recommended amount, provides 97 percent protection against measles. Yet some parents refuse to vaccinate their children, citing religious reasons or false information that vaccines cause autism.

Most recently, a study of more than 650,000 children from 1999 to 2010 found no link between autism and the MMR vaccine.