Nearly 200 students have been rushed into quarantine in North Dakota over fears they were exposed to measles.
The under-18s had all been in school buses or on campus at elementary, middle and high schools at the same time as four patients infected with the ultra-infectious disease.
All 180 students are unvaccinated, with officials saying they must now quarantine for 21 days — the time taken for symptoms of the virus to emerge.
Vaccinated students are not required to quarantine because they are considered to be protected, with two doses slashing the risk of infection by 97 percent.
The students will not leave quarantine until after term ends on May 23, but school principals say that if they aren’t infected they will be able to attend graduation ceremonies.
Williston Middle School and Williston High School are affected, as well as Missouri Ridge Elementary. Together, they have about 5,300 students.
It comes after the US crossed another grim milestone, with the CDC today confirmed that more than 1,000 measles cases have been diagnosed in the country. It puts the tally at 1,001 infections.
This marks only the second time the country has seen this many cases since the disease was declared eradicated nationwide in 2000, with some doctors now worried the country could lose its measles elimination status.