Utah state officials on Wednesday reported a total of 602 measles cases tied to an outbreak that began last year and remains active, including 19 newly identified infections, according to the Center for Infectious Disease Research and Policy. Recent exposures have been reported at several preschools and elementary schools in the state.

Of the 602 total cases, 405 have occurred since the beginning of this year, and 75 have been reported in the last three weeks. Of those infected, 513 people, or 85%, were not vaccinated against measles. Most cases in the outbreak occurred in children, many of whom had not received the measles, mumps and rubella vaccine.

About one-third of those infected experienced symptoms severe enough to require emergency room visits, largely due to dehydration from vomiting and diarrhea. So far, 49 individuals have needed hospitalization.

The spread of measles in Utah appears to be occurring more broadly across the general population, unlike many previous outbreaks that were often linked to close-knit religious communities. Approximately 90% of Utah residents are vaccinated against measles. Typically, about 95% vaccination coverage is needed to achieve herd immunity. Infants under one year old and children with certain health conditions remain especially at risk from measles even in communities with high vaccination rates.

Earlier this year, while the outbreak was active, state lawmakers introduced a bill to make it easier for families to opt out of school vaccination requirements. The proposal did not pass.

Over the past year, large measles outbreaks have occurred in multiple parts of the United States, including Texas and South Carolina. The outbreak originally began in Texas more than a year ago and has since spread to most states, ending the period when measles was considered eliminated in the U.S.