The World Health Organization on Monday advised against using the blood plasma of patients who have recovered from COVID-19 to treat those who are ill, saying current evidence shows it neither improves survival nor reduces the need for ventilators. The hypothesis for using plasma is that the antibodies it contains could neutralize the novel coronavirus, stopping it from replicating and halting tissue damage.Several studies testing convalescent blood plasma have shown no apparent benefit for treating COVID-19 patients who are severely ill. A U.S.-based trial was halted in March after it was found that plasma was unlikely to help mild-to-moderate COVID-19 patients. The method is also costly and time-consuming to administer, the WHO said in a statement Monday. A panel of international experts made a strong recommendation against the use of convalescent plasma in patients with non-severe illness, the WHO said. They also advised against its use in patients with severe and critical illness, except in the context of a randomized controlled trial. The recommendation, published in the British Medical Journal (BMJ), is based on evidence from 16 trials involving 16,236 patients with non-severe, severe and critical COVID-19 infection.