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LETTER: COVID-19 convalescent plasma treatment update

Letter to the editor

This is a follow-up to the guest opinion (Explore COVID-19 convalescent plasma treatment, Oct. 19), in which I reviewed the rationale for this treatment and presented some encouraging results based on exploratory analysis of data from a large FDA-Mayo Clinic study. We are still months away from having the pandemic under control by vaccination and it is premature to regard therapeutic options as superfluous.

Two research groups have directed efforts at evaluating convalescent plasma (CP) with high antibody levels when given early in the disease. One, from the eight-hospital Houston Methodist system, was published in November in the American Journal of Pathology. They compared treated hospitalized patients with carefully matched controls, and found a 67 per cent reduction in 60-day mortality in those who received high-antibody CP within 44 hours of admission (4 per cent vs 12.3 per cent). Treatment after 72 hours resulted in no significant benefit.

The second study is a randomized controlled trial (RCT) from Argentina. Results have just made it from preprint to the hallowed New England Journal of Medicine. Subjects were over 75, or 64-75 with at least one risk factor, who presented early with confirmed but mild illness. Overall, there was a 48 per cent reduction in progression to severe illness in CP recipients; in those given plasma with the highest antibody levels the reduction was 73 per cent.

Evidence thus far suggests that infusion of high-antibody CP can be as effective as commercial monoclonal antibody cocktails such as the one that U.S. President Donald Trump received promptly and seemingly benefited from.

An important consideration is the possible emergence of COVID-19 mutations that will not be fully susceptible to antibodies generated in response to current vaccines. CP from individuals who have recovered from a new strain would represent a treatment option, assuming rapid development of appropriate antibody measurement for donor assessment.

David Toms,

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