CAMBRIDGE, Mass.—Colleges across the nation began taking the unprecedented step of sending students home for the rest of the spring semester, as they struggled to respond to the escalating uncertainties of the novel coronavirus.

Harvard University Tuesday morning told students to move out of their campus housing no later than Sunday and not to return until further notice. Classes will be taught remotely. The school, which has no confirmed cases of the virus, has a regularly scheduled spring break next week.

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