An ambulance pulls away from London's Royal Free Hospital where Scottish nurse Pauline Cafferkey is in serious but stable condition.

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Condition of UK Ebola patient Pauline Cafferkey improves to "serious but stable"

The nurse suffered a relapse nine months after being discharged

She was in critical condition last week

London CNN  — 

The condition of a Scottish nurse battling a relapse of the deadly Ebola virus has improved, a London hospital says.

Pauline Cafferkey, 39, is in a “serious but stable” condition in London’s Royal Free Hospital, the National Health Service (NHS) said in a statement.

Cafferkey was admitted to hospital in Glasgow, Scotland, nearly two weeks ago due to “an unusual late complication” of her Ebola infection, according to the NHS.

She was transferred to a high-level isolation unit in a London hospital as her condition worsened, and by last Wednesday, health authorities said she was critically ill.

Cafferkey’s relapse came about nine months after she was first discharged from the Royal Free Hospital, having apparently beaten the virus.

The public health nurse contracted Ebola, which has killed more than 11,000 people internationally, while working as part of a 30-person team deployed by the UK government to work to contain the outbreak in Sierra Leone. She was diagnosed with Ebola shortly after returning to the UK.

British health officials have said that the risk to the public from Cafferkey’s relapse is “very low,” but that they have been following up with her close contacts.

A preliminary study released by the World Health Organization this month found that the virus can still be found in the semen of survivors for at least nine months after the onset of symptoms, and a U.S. Ebola survivor was found to have traces of the virus in his eye months after doctors had declared him Ebola-free.

READ MORE: Ebola virus found in male survivors 9 months after symptoms

CNN’s Greg Botelho contributed to this report.