Two elderly South Korean coronavirus patients recovered from severe pneumonia after being treated with plasma from survivors, researchers said Tuesday, offering hope in the face of the global pandemic.

Scientists have pointed to the potential benefits of plasma -- a blood fluid -- from recovered individuals who have developed antibodies to the virus enabling the body's defences to attack it. Since emerging in China in December, the coronavirus has killed almost 75,000 people as drugmakers worldwide race to develop a vaccine and treatments for the disease.

Plasma therapy could become "an alternative treatment for patients in critical condition who do not respond to antiviral drugs," said Choi Jun-yong, a doctor and researcher at Severance Hospital in Seoul, where both patients were treated.

But large-scale clinical trials were needed to prove its effectiveness, he added. One of the two patients was a 71-year-old man with no underlying conditions who only improved when treated with plasma from a recovered patient in his 20s, along with steroids.

He was initially given malaria drugs and a respirator for severe pneumonia. The other patient, a 67-year-old female, also did not respond to initial treatments including malaria, HIV drugs, and oxygen therapy. She began to recover after receiving plasma therapy and steroids at the same time, researchers said.

Their findings were published in the peer-reviewed Journal of Korean Medicine.

Kwon Jun-wook, an official at Seoul's Central Disease Control Headquarters, said plasma therapy was "important" when there was "currently no vaccine or treatment available" for the virus.

He called on experts to examine the two cases urgently. Research on plasma and other therapies "will proceed quickly", Kwon added.

Small studies on plasma have demonstrated its effectiveness in treating infectious diseases, including Ebola and SARS. Trials started in France on Tuesday involving 60 patients in Paris hospitals, half of whom will receive plasma from recovered patients.

The US Food and Drug Administration authorised physicians to experiment with the strategy to fight the coronavirus, and tests are also being carried out in China. South Korea endured one of the worst early outbreaks of the virus, but appears to have brought it under control thanks to its extensive "trace, test and treat" programme.