The US National Institutes of Health (NIH) has put on hold a trial of convalescent blood plasma in treating patients with mild-to-moderate Covid-19 symptoms as the study provided no significant benefit in this group.

Covid-19 convalescent plasma is the blood plasma obtained from individuals who have recovered from the disease. Also known as survivor’s plasma, it has the body’s immune system-generated antibodies or special proteins to the novel coronavirus.

The latest decision is based on the findings of an independent data and safety monitoring board (DSMB).

Named ‘the Clinical Trial of COVID-19 Convalescent Plasma of Outpatients (C3PO)’, the study was launched last August at 47 hospital emergency departments across the US. It enrolled 511 subjects out of its goal of 900 participants.

It analysed the effectiveness of Covid-19 convalescent plasma in adult individuals with mild to moderate symptoms developed in a week or less.

In addition, the subjects had at least one risk factor linked to severe Covid-19, such as obesity, hypertension, diabetes, heart disease, or chronic lung disease, but were not sick enough to be hospitalised.

The study subjects were given either the Covid-19 convalescent plasma or placebo and were monitored to check if they required further emergency care, hospitalisation, or died within 15 days of entering the trial.

No significant difference in the proportion of subjects who experienced any one of these outcomes was observed in the latest data analysis from the study.

On 25 February, the panel met for the second planned interim analysis of the trial data and recommended that the convalescent plasma intervention caused no harm but provided no benefit to these subjects.

After the meeting, the DSMB advised the NIH unit National Heart, Lung, and Blood Institute (NHLBI) to discontinue enrolment of new patients into the study. NHLBI implemented the advice immediately.

NIH noted that even if more patients were enrolled in the study, the trial was not likely to show that Covid-19 convalescent plasma prevents disease progression from mild to severe illness in at-risk emergency department non-hospitalised subjects.