The U.S. reported a total of 704 cases of measles so far in 2019 - the greatest number since 1994.
Seventy-eight new cases were reported last week, the U.S. Centers for Disease Control and Prevention (CDC) said Monday. Though no deaths have been reported, 66 people were hospitalized.
Thirteen specific outbreaks have been identified by the CDC, and of those six were associated with "underimmunized close-knit communities", which accounted for 88% of all cases, according to Monday's CDC report.
One such example is the outbreak in New York, which has been traced to Orthodox Jews who contracted the disease while traveling overseas. Cases have been reported in 22 states.
The CDC recommends vaccinations for everyone over a year old, except those who contracted measles as children and have since become immune.
The vaccine, which first became available in the 1960s, is considered safe and effective by most public health experts. Measles spreads through the air when an infected person coughs or sneezes. The disease was considered eradicated from the United States in 2000.