The final results of the Clinical Trial of COVID-19 Convalescent Plasma in Outpatients (C3PO) demonstrate that COVID-19 convalescent plasma did not prevent disease progression in a high-risk group of outpatients with COVID-19, when administered within the first week of their symptoms. The trial was stopped in February 2021 due to lack of efficacy based on a planned interim analysis. The formal conclusions from the trial, which was funded primarily by the NHLBI, appeared The New England Journal of Medicine.
“The results show that convalescent plasma does not appear to benefit this particular group,” said Nahed El Kassar, M.D., Ph.D., one of the study’s co-authors and medical officer in the Blood Epidemiology and Clinical Therapeutics branch of the NHLBI’s Division of Blood Diseases and Resources. “But the findings answer an important clinical question and may help bring researchers a step closer to finding more effective treatments against this devastating disease.”
The C3PO trial, launched in August 2020, was a randomized, controlled clinical trial that involved adult outpatients who presented to emergency departments with mild COVID-19 symptoms during their first week post-infection. The trial enrolled more than 500 participants from 48 emergency departments across the United States. The participants were racially and ethnically diverse with a median age of 54 years, and slightly more than half were women. Participants also had at least one risk factor for progression to severe COVID-19, such as obesity, hypertension, diabetes, heart disease, or chronic lung disease. The researchers randomly assigned the participants to receive treatment with either high-titer COVID-19 convalescent plasma (containing anti-COVID-19 antibodies) or placebo (salt solution infused with multivitamins and lacking antibodies).
Researchers compared outcomes in both groups within 15 days of treatment, looking specifically at whether the patients needed to seek further emergency or urgent care, were admitted to the hospital, or died. The researchers found no significant difference in disease progression between the two groups. Of the 511 participants, disease progression occurred in 77 (30%) in the COVID-19 plasma group compared with 81 patients (31.9%) in the placebo group. The plasma intervention did not cause harm, the researchers found.
Additional studies of COVID-19 convalescent plasma are ongoing or planned in different populations. “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,” said Simone Glynn, M.D., M.P.H., chief of the NHLBI’s Blood Epidemiology and Clinical Therapeutics branch, who coordinated the C3PO trial.