University officials initially said it was unlikely that the students would get the disease because the students said they had not come in contact with any Ebola patients while they were in Liberia. Ebola is spread through bodily fluids.

Earlier in the day, Yale’s president, Peter Salovey, sought to allay fears, emailing a message to students, faculty and staff.

“The doctoral students who visited Liberia are knowledgeable about public health,” Dr. Salovey wrote. “They have reported that they were not in contact with Ebola patients or caregivers in Liberia, that they carefully followed recommended travel and hygiene precautions during their stay in the country and that they have continued to do so since their return.”

The officials did not discuss the whereabouts or condition of the other student who went on the research mission.