The treatment contains antibodies that should help fight the infection.
British nurse William Pooley has donated plasma, Chief Medical Officer Dame Sally Davies confirmed.
Other available treatments include antiviral drugs, but there are no stocks left of ZMapp – the drug used to treat Mr Pooley.
He recovered from Ebola in September after being treated at the Royal Free Hospital, in Hampstead, north London, where Ms Cafferkey is currently being cared for.
Having fought off the infection, his blood should help others do the same.
Dame Sally said it would be up to Ms Cafferkey and her doctor to decide which treatments to use, adding: “The cornerstone of treatment remains fluid and electrolyte treatment.”
Ms Cafferkey was diagnosed with Ebola after returning to Glasgow from Sierra Leone, where she had travelled with a group of healthcare workers from Save the Children.
She was said to be doing “as well as can be expected under the circumstances” by Scotland’s First Minister Nicola Sturgeon.
Another healthcare worker who was recently in West Africa and fell ill in the Scottish Highlands has tested negative for the disease.
Dame Sally said that Ms Cafferkey was in the early phase of the disease when she made the journey to the UK from Sierra Leone, via Casablanca, and her fellow passengers were at “very low risk” of being infected.
She had no detectable fever or symptoms. Anyone displaying symptoms at screening, either in Sierra Leone or in the UK, would not have been allowed to travel.
One-third of the 132 other passengers on the flight from Casablanca to Heathrow have been contacted by Public Health England, while advice has been given to more than half the 72 passengers from Heathrow to Glasgow, officials said.
Those sitting in the two rows adjacent to, ahead and behind Ms Cafferkey will be advised to keep a check on their temperature for the next few weeks and to contact officials if they get a fever or feel unwell.
Concerns about the Ebola screening process at Heathrow have been raised by Dr Martin Deahl, a consultant psychiatrist who travelled back on the same flight as Ms Cafferkey.
He described the screening as “chaotic”, claiming there were too few staff on duty and the rooms where returning volunteers were held were too small.
Dame Sally said procedures for detecting the disease are being reviewed, but said the correct protocols had been followed.
Save the Children, the charity with which Ms Cafferkey volunteered, issued a statement saying: “We have robust and strict protocols in place to protect our staff.
“Save the Children also asks staff to be careful outside of the treatment centre, where exposure to risks can be less obvious.”
Ms Cafferkey had her temperature checked seven times while at Heathrow before she was cleared to continue on her journey to Glasgow.
Ebola is transmitted by direct contact with the bodily fluids of an infected person, such as blood, vomit or faeces.
The virus has killed more than 7,800 people, mostly in West Africa, since it broke out a year ago.
The World Health Organization says the number of people infected by the disease in Sierra Leone, Liberia and Guinea has now passed 20,000.
The early symptoms are a sudden fever, muscle pain, fatigue, headache and sore throat.
This is followed by vomiting, diarrhoea, a rash and bleeding – both internal and external – which can be seen in the gums, eyes, nose and in the stools.
Patients tend to die from dehydration and multiple organ failure.