The World Health Organisation (WHO) has said Covid treatments using plasma taken from the blood of recovered coronavirus patients should not be given to people with mild or moderate illness, AFP reports.

Convalescent plasma showed some early promise when given intravenously to people sick with Covid-19. But in advice published in the British Medical Journal, the WHO now says that “current evidence shows that it does not improve survival nor reduce the need for mechanical ventilation, and it is costly and time-consuming to administer”.

It made a “strong recommendation” against the use of blood plasma in people who do not have serious Covid-19 symptoms and said that even for patients with severe and critical illness, the treatment should only be given as part of a clinical trial.