Despite its initial promise as a breakthrough treatment for COVID-19, convalescent plasma therapy does not improve the survival rate of COVID patients, and it does not reduce the need for ventilation in severe cases, the WHO says. It based that conclusion on a British Medical Journal study trial involving 16,000 COVID-19 patients.

On that basis, and given the fact that it is costly and time-consuming to administer, they recommend against its use.

Blood plasma therapy has been considered a possible treatment for COVID-19 since the onset of the pandemic, and trials conducted by the European Union, Russia, Japan, and others have been trying to prove its efficacy.

In the U.S., the Food and Drug Administration first put approval of blood plasma therapy on hold in November 2020 after a Mayo Clinic trial found it did not help in the treatment of COVID-19. At the time, Donald Trump hailed the treatment as a “beautiful ingredient” coming from the veins of people who have survived COVID-19. The former president went on to criticize any holdup in approving the treatment.

“You have a lot of people over there who don’t want to rush things, because they want to do it after November 3,” he said last year, referring to Election Day, noting the convalescent plasma had already helped “way over 50%” of COVID-19 patients infused with it.

Regulators in August 2020 then granted emergency authorization for these infusions, but only for hospitalized patients. The following month, experts convened by the U.S. National Institutes of Health broke with the Food and Drug Administration, noting there wasn’t enough evidence to recommend it as a viable treatment.

In many ways, the WHO has taken a more deliberate approach to ruling on its merits. There have been previous trials that found the same underwhelming results for convalescent plasma therapy. A study by Nature Medicine, published in September, found that patients hospitalized with COVID-19 who received convalescent plasma did not see a reduction in the risk of intubation or mortality.

More recently this month, the COVID-19 Convalescent Plasma in Outpatients trial published its results, which found infusing high-tier COVID-19 convalescent plasma within seven days after onset of symptoms did not prevent COVID-19’s progression in patients at high risk for severe disease.

The authors of the report did, however, note that the treatment could still be beneficial in certain cases but that more research was needed.