It's already the highest in 27 years.
The Centers for Disease Control and Prevention updated the count Wednesday, saying 1,001 illnesses have been reported since the beginning of the year. Most are from outbreaks in New York in Orthodox Jewish communities.
The nation last saw this many cases in 1992, when more than 2,200 were reported.
Overall vaccination rates have remained fairly high, but outbreaks have been happening in communities where parents have refused recommended shots for their children.