Treating coronavirus patients in hospital with a high level of antibodies from the blood plasma of recovered patients could greatly reduce mortality, according to a large-scale study run by the Mayo Clinic in the United States.
The study enrolled 35,322 patients treated with such therapy in 2,807 acute care facilities in the US from early April to early July. More than half the enrolments were in the intensive care unit and 27.5 per cent had to breathe with the help of mechanical ventilation at the time of the plasma transfusion.
The study found the early administering of such plasma, called convalescent plasma and donated by recently recovered patients, significantly helped the seriously ill patients
Those who received transfusions – around 200 millilitres or more – within three days of diagnosis had a seven-day death rate of 8.7 per cent while patients who got plasma after four or more days had a mortality rate of 11.9 per cent. The difference is statically significant.
The study also observed a correlation between the level of antibodies in the transfused plasma and mortality.
For 80 patients who received a high level of IgG in plasma the seven-day mortality was 8.9 per cent, whereas for recipients of medium IgG plasma mortality was 11.6 per cent and 13.7 per cent for recipients of low IgG plasma. IgG (Immunoglobulin G) is a common type of antibody.
“The finding of a dose response between antibody levels and reduction in mortality provides strong evidence that specific antibody is the active agent in convalescent plasma for treatment of Covid-19,” the authors wrote.
All data considered as a whole, these findings were consistent with the notion that the quality and manner in which convalescent plasma was administered to patients admitted to hospital with Covid-19 might reduce mortality, they added.
Plasma infusion has long been a treatment for infectious diseases involving the respiratory system, including being used in the 1918 influenza pandemic and the more recent Sars (evere scute respiratory syndrome) outbreak in 2002-03 and the H7N9 bird flu in 2013.
The treatment is based on the understanding that rich antibodies from recovered patients help struggling patients fight the disease.
Some pharmaceutical companies have been working to develop lab-grown Covid-19 antibodies based on the same theory and several are in the clinical trial phase. The immunity gained from such treatment does not last.
The Mayo Clinic data has not been published in a journal or been subjected to peer review. It was published on a preprint site, medRxiv.org, on Thursday. Dr Michael Joyner from the Mayo Clinic was the principal investigator of the study.
The study was not a randomised placebo, controlled trial, making it difficult to evaluate how useful it is. Smaller randomised, placebo-control studies of convalescent plasma are under way.
The authors acknowledged the limitations of the study. They said they had analysed the data from 1,809 sites and noted there was variability in the time to transfusion after diagnosis.
Researchers had no information about antibody levels in the convalescent plasma when they were being administered, contributing to “inherent randomisation” in the data collection.
The authors said it was difficult to design a randomised controlled trial because of limitations on both access to a stable supply of the plasma product and access to an “appropriate patient base”.
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This article was first published in South China Morning Post.