Doctors say they have found 'some evidence' that plasma from the blood of coronavirus survivors could help those seriously ill with Covid-19 to recover.

Here's everything we know so far.

How does the treatment work?

Convalescent plasma - rich in antibodies - is taken from patients who have recovered from coronavirus and given by blood transfusion to those who are still seriously ill.

The treatment is not new, and dates back to before the 1918 Spanish flu pandemic.

The reason it can be effective is that people who have recovered from a viral infection have antibodies in their blood which can more easily detect and destroy the virus, in the event that it should attack again.

Giving these antibodies to patients who remain ill can, therefore, boost their immune systems and provide protection.

This treatment may also be used to protect people who are in high risk groups.

How effective is it?

Two teams of medics fighting coronavirus in China piloted the treatment, giving plasma to 15 severely ill patients and recording improvements in many.

In the pilot study, 10 patients were given the plasma. Virus levels were found to drop rapidly in the patient's bodies, and within three days, doctors saw improvements in symptoms ranging from chest pain to shortness of breath.

In another study, plasma was given to five critically ill patients at China's Shenzhen Third People's hospital.

Every patient showed an improvement in symptoms and, within 10 days, three out of the five were able to come off the ventilators that had been keeping them alive, according to a report in the Journal of the American Medical Association.

Some trials have also begun elsewhere, with Professor David Tappin (a senior research fellow at the University of Glasgow) applying to the UK’s National Institute for Health Research to run two UK trials using plasma.

In spite of this, the trials of the treatment have been small so it's difficult to know both how effective the treatment is and whether it can be scaled up at this stage.

It would also need to go through formal trials before it could be administered widely.

What do the experts say?

Professor Munir Pirmohamed, the president of the British Pharmacological Society, told the Guardian that it's important not to jump the gun with this treatment.

“This was not a randomised trial and all patients also received other treatments including antivirals such as remdesivir, which are currently in trials for Covid-19,” he said.

“It is also important to remember that there are potential safety concerns with convalescent plasma, including transmission of other agents and antibody enhancement of disease.

“Even if shown to work, scalability to treat large numbers of patients may become an issue.”