COVID-19 Update, 24 August 2020: Absolute versus Relative Risk

The Trump Administration today has taken up the call of the convalescent serum “breakthrough” by spreading the notion that this treatment would save 30-50 individuals out of 100 infected with COVID-19. This is false and those saying such have made a fundamental error in mistaking absolute risk for relative risk. Relative risk is a basic Epidemiologic concept covered in any first year, introductory class.

Some examples of the false soundbites:

1. Michael Caputo (Health and Human Services Assistant Director – no medical training): “If you’re one of the 35 people out of a hundred who survive severe COVID symptoms because of convalescent plasma, you’re damn right this is a BREAKTHROUGH.”

2. Alyssa Farah (White House Director of Communications – BA in Journalism and Public Policy, no medical training): “Mayo Clinic shows Convalescent Plasma will reduce mortality from COVID by as much as 30 to 50%. These are REAL American lives that will be saved as a result of this EUA.”

The Mayo Clinic study reported that convalescent serum reduced the 7-day death rate from 11.9% to 8.7%, not that it would “stop” 35 out of 100 deaths. In reality, 3 more people out of 100 may survive when treated, not 35. Or, to put more bluntly, 97 of 100 would still be expected to die.

Convalescent serum is not a miracle. Treatment of severe COVID-19 manifestations are best treated with prone positioning, oxygen support, dexamethasone, antithrombotics to prevent clots, and remdesivir (an antiviral originally developed for Ebola). Convalescent serum still has a role in compassionate use scenarios – but 97 out of 100 patients relying on its efficacy alone will still die.

Those are the facts.

Mayo Clinic Studies:

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