The results of a major trial testing convalescent plasma therapy for COVID-19 in high-risk outpatients have been published in The New England Journal of Medicine. The once-promising therapy was found to be ineffective in preventing disease progression in high-risk patients.
As doctors looked for any kind of way to help patients in the early phases of the COVID-19 pandemic many optimistically turned to an old 19th century therapy – using blood transfusions from recovered patients to treat those with acute infections. Known today as convalescent plasma therapy, the idea is antibodies present in the blood of recovered patients can help those suffering acute disease.
A major trial was established by the National Institutes of Health (NIH) to explore the efficacy of this treatment. Called C3PO (the Clinical Trial of COVID-19 Convalescent Plasma in Outpatients), the plan was to test the treatment on 900 patients at a high-risk of severe COVID-19. The patients were recruited and treated early on in the course of the disease, upon presenting at a hospital emergency room as an outpatient with COVID-19 within seven days of symptoms initially arising.
An independent interim analysis of the trial early in 2021 called a halt to the study after 511 patients had been enrolled. Despite the treatment being found to be safe, no benefit was detected between treatment and placebo groups up to that point. Now the full data has been peer-reviewed and published offering greater insights into the trial’s results.
Conducted in 48 emergency room departments across the United States the trial recruited subjects as they presented to an ER with mild COVID-19 symptoms. The median age of the cohort was 54 and all participants had at least one condition – such as diabetes, obesity or heart disease – putting them in a high-risk category for severe disease.
While in the emergency room half the cohort were administered a transfusion of convalescent plasma with high volumes of SARS-CoV-2 antibodies, and the other half were administered a placebo salt solution transfusion. Patients were then sent home and outcomes were tracked for the following few weeks to establish whether the blood transfusion reduced the risk of further hospital care.
Virtually no differences in disease progression were noted between plasma and placebo groups. Around 30 percent of those in the plasma group required further hospital care for COVID-19 compared to 31.9 percent in the placebo group. Illness severity was also similar in both groups and five patients in the plasma group ultimately passed away compared to one in the placebo group.
“We were hoping that the use of COVID-19 convalescent plasma would achieve at least a 10 percent reduction in disease progression in this group, but instead the reduction we observed was less than 2 percent,” says Clifton Callaway, a principal investigator on the C3PO trial. “That was surprising to us. As physicians, we wanted this to make a big difference in reducing severe illness and it did not.”
The new data is not the end for research into convalescent plasma for treating COVID-19 despite other recent trial failures. Several ongoing clinical trials are set to deliver results in the coming months exploring other targets for the treatment, including whether it prevents infection in subjects exposed to the virus but yet to test positive, or whether it accelerates recovery in mild to moderate cases treated at home.
“We need the results of these other convalescent plasma studies to get a clearer, more conclusive picture of its value for future treatments of COVID-19,” explains Simone Glynn, a researcher from NIH’s National Heart, Lung, and Blood Institute.
The new study was published in The New England Journal of Medicine.