A nurse who recovered from Ebola last year has been hospitalized again for treatment of an unusual late complication, London’s Royal Free Hospital said Friday. Pauline Cafferkey was being treated in the hospital’s isolation unit and her condition was described as serious.

Ben Neuman, a virologist at the University of Reading, said, Cafferkey’s case appeared unusual because of the stubborn persistence of the Ebola virus in her body. In a similar case detected in an American doctor, Ebola was found in his left eye months after he recovered. Cafferkey was flown to London early Friday from Scotland, where she lives.

Medical authorities say the risk of Cafferkey transmitting the virus is low, but public health officials in Scotland are monitoring people with whom she had close contact. Ebola is transmitted by direct contact with blood or body fluids. Cafferkey was diagnosed with Ebola in December after returning from Sierra Leone. She was treated at the Royal Free for several weeks and discharged in January. Cafferkey was honored at the Pride of Britain Awards in London last month and met with Prime Minister David Cameron’s wife, Samantha, at 10 Downing St.

The prime minister tweeted that he wished Cafferkey “a quick recovery.” Since Ebola broke out in Guinea’s forest region last year, it has killed more than 11,200 people in West Africa. Experts say there is mounting evidence that the mental and physical health problems in Ebola survivors can last for years after the virus is cleared from the bloodstream. There are thousands of Ebola survivors in West Africa suffering from long-term side effects of the disease, many of whom have no access to treatment.