Convalescent Plasma Does Not Reduce Risk of Intubation, Mortality

The antibody profile in the blood of patients who have had the virus is extremely variable and this may modify the response to the treatment.

Hospitalized patients with COVID-19 who were treated with convalescent plasma did not see a reduction in the risk of intubation or mortality, according to a new study.

“It has been thought that the blood plasma of COVID-19 survivors would help those seriously ill from the virus but, unfortunately, it does not,” Donald Arnold, co-principal investigator of the study, hematologist and professor of medicine at McMaster University, said. “We are cautioning against using convalescent plasma to treat COVID-19 hospitalized patients, unless they are in a closely-monitored clinical trial.”

The study results were published in the journal Nature Medicine.

The clinical trial, called CONCOR-1, stopped enrollment early in January 2021 after its independent data safety monitoring committee recommended the study was unlikely to demonstrate a benefit of convalescent plasma even if more patients were enrolled.

Investigators also found that patients receiving convalescent plasma experienced significantly more serious adverse events than those receiving standard care.The majority of those events were an increased need for oxygen and worsening respiratory failure. However, the rate of fatal incidents was not significantly different from the control group of patients who did not receive the blood.

A secondary discovery was that convalescent plasma had highly variable donor antibody content due to the highly variable immunological response to the virus. Different antibody profiles in the convalescent plasma were observed to significantly impact whether or not patients experienced intubation or death. Unfavorable antibody profiles, meaning low antibody titers, non-functional antibodies or both, was associated with a higher risk of intubation or death.

“These findings may explain the apparent conflicting results between randomized trials showing no benefit, and observational studies showing better outcomes with higher titer products relative to low titer products,” Jeannie Callum, co-principal investigator, associate scientist at the Sunnybrook Research Institute, and professor at Queen’s University and the University of Toronto, said. “It appears that it may not be that high-titer convalescent plasma is helpful, but rather that low-titer convalescent plasma is harmful.”