Officials at the National Institutes of Health (NIH) in the US on Tuesday stopped an ongoing clinical trial using blood plasma from patients who recovered from the coronavirus disease 2019 (Covid-19) to treat severe Covid-19 cases, due to lack of clear clinical benefit.

The trial, which focused on emergency-room patients with mild to moderate symptoms of infection, found the approach to be safe, the agency said.

However, the treatment, which relies on blood plasma collected from patients who have recovered from Covid-19, did not speed recovery or lead to a significant reduction in symptoms.

“The National Institutes of Health has halted a clinical trial evaluating the safety and effectiveness of … convalescent plasma in treating emergency department patients who developed mild to moderate symptoms of Covid-19,” the agency said in a statement.

“Study shows the treatment is safe, but provides no significant benefit in this group,” it said.

The NIH made the decision based on the recommendation of an independent data and safety monitoring board, which delivered its findings on Feb. 25, 2020.

The board recommended that the National Heart, Lung, and Blood Institute, which is part of the NIH and was leading the trial, stop enrolling new patients, and the agency “did so immediately,” it said.

Convalescent plasma has been suggested as a possible treatment for Covid-19 since the start of the pandemic, and it has been used in more than 100,000 people worldwide.

It operates on the theory that plasma from patients who have recovered from infection have antibodies against in their blood.

By transfusing blood from recovered donors into patients currently battling the disease, it was thought that these antibodies would help boost recipients’ immune systems.

Studies of monoclonal antibodies, or lab-created immune cells against the virus, are currently being evaluated, and one such treatment has already received an emergency use authorization from the Food and Drug Administration.

TRIALS SINCE AUGUST LAST YEARS

Launched in August 2020, the Clinical Trial of Covid-19 Convalescent Plasma of Outpatients, called C3PO, was being conducted in 47 hospital emergency rooms across the country.

At the time of Tuesday’s announcement, the trial had enrolled 511 of the planned 900 participants, officials said.

The trial “was specifically looking at the effectiveness of Covid-19 convalescent plasma in adults who came to an emergency department with mild to moderate symptoms they had for a week or less,” according to the NIH.

“These patients also had at least one risk factor associated with severe Covid-19, such as obesity, hypertension, diabetes, heart disease or chronic lung disease, but none were ill enough at the time to be hospitalized,” the agency said.

Study participants received either Covid-19 convalescent plasma or a placebo, according to the agency.

At least to date, there was “no significant difference in the proportion of participants” within the two groups who needed to seek further emergency or urgent care, had to be hospitalized or died within 15 days of entering the trial, the data showed.

“Even if enrollment continued, this trial was highly unlikely to demonstrate that Covid-19 convalescent plasma prevents progression from mild to severe illness in at-risk emergency [room] non-hospitalized participants,” the NIH said.