The World Health Organization (WHO) is strongly advising against the use of convalescent plasma to treat COVID-19 patients, because research shows no improved chance of survival in people who undergo the treatment.

"Current evidence shows that convalescent plasma does not improve survival or reduce the need for mechanical ventilation, while it has significant costs," the WHO said in a statement issued Monday.

Convalescent plasma is a transfusion of blood plasma taken from someone who has recovered from COVID-19 to help treat others. 

An independent panel of experts looked at pooled data from 16 randomized controlled trials of more than 16,000 patients with non-severe, severe and critical COVID-19 infection.

The group said the evidence that convalescent plasma has no benefit in non-severe patients was certain, but severe and critically ill patients should use it within a clinical trial. 

"Given the number of patients with non-severe disease and the low event rate in this subgroup of patients, mobilizing the use of convalescent plasma on a large scale, would be of questionable feasibility," the WHO said.

A Food and Drug Administration (FDA) spokeswoman said the agency is aware of the WHO's decision but was not going to comment on it. The FDA's current emergency authorization for the treatment remains in effect.

Last February, the FDA significantly scaled back its authorizations of convalescent plasma, to limit its use to hospitalized patients early in the progression of the disease.

The agency also limited the treatment to patients hospitalized who have immune system disorders in which they cannot produce a strong antibody response.

The initial authorization, issued in August 2020, was for all hospitalized patients. At the time, then-President Trump praised the treatment as a “historic breakthrough” in fighting the coronavirus, and said it had “an incredible rate of success.”

The authorization came amid concerns from health experts about an array of politically motivated moves by health agencies responding to pressure from Trump.