U.S. President Donald Trump speaks to reporters before boarding Air Force One for travel to Indianapolis, Indiana, at Joint Base Andrews, Maryland, outside Washington, D.C, April 26, 2019.
U.S. President Donald Trump speaks to reporters before boarding Air Force One for travel to Indianapolis, Indiana, at Joint Base Andrews, Maryland, outside Washington, D.C, April 26, 2019.

President Donald Trump urged Americans Friday to get vaccinated against measles, amid an outbreak of the highly contagious virus in the U.S. that has forced two U.S. universities to quarantine hundreds of students, faculty members and other employees.

Trump told reporters at the White House citizens "must get their shots" to protect themselves against the virus that was deemed eradicated in the U.S. nearly 20 years ago.

There were nearly 700 cases in 22 states, the Centers for Disease Control (CDC) reported Wednesday, the highest level in 25 years. The CDC partially attributed the surge to misinformation about the safety of the measles vaccine.

The beginning of the outbreak has been traced to Orthodox Jews who contracted the disease while traveling overseas. The cases have been concentrated in a small number of states, including New York, New Jersey, Michigan and Washington.

Sign advertising free measles vaccines and informa
Signs advertising free measles vaccines and information about measles are displayed at the Rockland County Health Department in Pomona, New York, March 27, 2019.

Cases also have been confirmed in California, where public health officials ordered dozens of people to be quarantined Tuesday at the University of California at Los Angeles and California State University, Los Angeles following an exposure to the virus earlier this month. Los Angeles County public health officials said some people may have to be quarantined up to one week until proof of immunity is established.

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.