More than 2,200 students were sent letters to get vaccinated.

A measles outbreak has prompted officials of the Seattle Public Schools to take the drastic action of ordering thousands of students to get vaccinated immediately or risk being barred from returning to classes after the winter break.

The school district sent out a letter to 2,274 students warning they will be kept out of school if they fail to provide a medically verified record
they received their immunization shots by the time classes resume on Jan. 8.

“If a student is excluded from school because of immunization requirements, the missed days will be recorded as unexcused absences,” according to a statement on the school district’s website.

The district scheduled three free clinics at Seattle schools to provide students with measles, mumps and rubella vaccination, officials said.

“Unfortunately, by state law we have to exclude them,” Tim Robinson, spokesman for the Seattle Public Schools, told ABC affiliate KOMO-TV in Seattle of any student who fails to get vaccinated. “They would be excluded here, they would be excluded at any school district, and we certainly want to avoid that. I know all schools want to avoid it because you don’t want students to miss any school time.”

A measles outbreak across the nation has hit the state of Washington particularly hard.

The state has been coping with two measles outbreaks this year in which 87 cases were confirmed, according to the Washington State Department of Health.

Earlier this year, the Washington Legislature passed a law removing “personal preference” as an exemption for the measles, mumps and rubella vaccination. Now only “religious” and “medical” exemptions are allowed, under the new law.

Robinson said the district has come up with a plan for dealing with any non-exempt student who shows up to school without having gotten vaccinated.

“If they come to school, we certainly have a plan in place that if a student comes to school on the 8th and their records aren’t up to date, they’ll just be held aside, their parents or guardian will be contacted,” Robinson said.

From Jan. 1 to Dec. 5, 2019, 1,276 individual cases of measles were confirmed in 31 states, the greatest number of cases reported in the United States since 1992, according to the Centers for Disease Control and Prevention. There were more cases of the infectious disease this year than there have been in the four years prior combined.

The CDC reported that 124 of the people who contracted measles this year were hospitalized, including 61 who suffered complications such as pneumonia and encephalitis.

Just last week, five U.S. airports, including Chicago’s busy O’Hare International Airport, had travelers pass through with confirmed cases of measles this month, exposing an unknown number of fellow passengers to the highly infectious disease, according to health officials in those cities.

This year’s measles outbreak was worse from a global standpoint. As of mid-November, the number of measles cases that countries around the world reported to the World Health Organization was three times higher than the number of cases reported during the same time in 2018.

ABC News’ Erin Schumaker contributed to this report.