The World Health Organization (WHO) said Tuesday that Covid treatments using plasma taken from the blood of recovered coronavirus patients should not be given to people with a mild or moderate illness.

Convalescent plasma showed early promise when administered intravenously to Covid-19 patients.

But in advice published in the British Medical Journal, WHO now affirmed 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.

According to WHO, the latest recommendations are based on evidence from 16 trials involving 16,236 patients with non-severe, severe, or critical Covid-19 infection.

It is worth noting that the Food and Drug Administration (FDA) had issued on August 23 an emergency use authorization (EUA) for convalescent plasma therapy to treat COVID-19 despite a wave of criticism.

What is convalescent plasma?

Convalescent plasma is the liquid portion of a recovered Covid patient's blood that contains antibodies produced by the body after infection.

According to FDA, the first treatment consists of injecting a little less than 8 ounces of plasma over a 1- to 2-hour period. Additional plasma infusions, on the other hand, "may occur during your hospital stay if the treating physician determines that additional treatments are clinically justified."