At least 153 students from two schools in South Carolina are under quarantine for 21 days due to measles exposures, state health officials announced.

The quarantined students were not vaccinated, officials added. The schools are both located in Spartanburg County: Global Academy of South Carolina and Fairforest Elementary. The outbreak has grown to at least eight measles cases, with a total of 11 cases reported overall in the state this year.

The U.S. has reported at least 1,563 measles cases this year – the highest number since 1992, the latest Centers for Disease Control and Prevention data show. There have been 44 measles outbreaks reported this year. In comparison, 16 outbreaks were reported last year.

It comes amid declining MMR (measles, mumps, and rubella) vaccination rates nationwide. Over 95% of kindergarteners were vaccinated with the MMR shot prior to the pandemic. That figure has now fallen to 92.5% in the most recent school year.

The lower rates leave an estimated 286,000 kindergarteners without protection from measles.