In early 2020, prior to the availability of either monoclonal antibodies or antiviral drugs, convalescent plasma was tested in what was called the “Mayo Clinic study,” even though the study involved more than 2,800 hospitals in the United States. The study, which involved treating patients with convalescent sera that contained high or low quantities of SARS-CoV-2 virus neutralizing antibodies, found a 35% relative risk reduction in progression to serious illness.

In the May 5, 2022, issue of the New England Journal of Medicine, researchers at the Bloomberg School of Public Health in Baltimore compared 1,181 patients who were randomized to receive plasma from patients convalescing from COVID-19 or control plasma. Patients were recruited from 23 sites in the United States and treated within nine days of the development of symptoms; most were unvaccinated. Like the Mayo Clinic study, researchers found a relative risk reduction for progressing to severe disease of 54% for those who received convalescent plasma (Sullivan DJ, Gebo KA, Shoham S, et al. Early Outpatient Treatment for Covid-19 with Convalescent Plasma. N Engl J Med. 2022 May 5;386:1700-1711.).

Beginning on April 16, 2020, the FDA encouraged blood donations from people who had recovered from COVID. Called the Expanded Access Program, between April and August 2020, tens of thousands of people sought to help others by donating their blood. Convalescent plasma usage peaked in the fall of 2020, with more than 40% of inpatients receiving the product. By March 2021, however, fewer than 10% of patients were receiving these lifesaving antibodies. The retreat from convalescent plasma, which was unfortunate, was estimated to have caused 29,000 excess deaths between mid-November 2020 and February 2021.

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