Health officials on Monday said 555 measles cases have been confirmed so far this year, up from 465 as of a week ago.
WATCH: How to avoid measles
While 20 states have reported cases, New York has been the epicenter. Nearly two-thirds of all cases have been in New York, and 85% of the latest week's cases came from the state. Most of the New York cases have been unvaccinated people in Orthodox Jewish communities.
The 2019 tally is already the most since 2014, when 667 were reported. The most before that was 963 cases in 1994.
The Centers for Disease Control and Prevention recommends that all children get two doses of measles vaccine, which is 97% effective.
Other states reporting measles cases this year include Arizona, California, Colorado, Florida, Georgia, Illinois, Indiana, Kentucky, Maryland, Massachusetts, Michigan, Missouri, Nevada, New Hampshire, New Jersey, Oregon, Texas and Washington. After the CDC issued its report Monday morning, Iowa officials said they too had seen a case.
Also on Monday, the World Health Organization reported that globally there are four times as many measles cases so far this year as there were at the same time last year.
Over the last year, the largest numbers have been in Ukraine, Madagascar and India, with each reporting more than 60,000 cases.