Convalescent Plasma antibody levels and the risk of death from COVID-19

a Mayo Clinic lab researcher with medical gloves, a face mask and protective eye wear holding a clear bag of golden yellow convalescent plasma

ROCHESTER, Minn. – Mayo Clinic researchers and collaborators have found an association between administration of convalescent plasma containing high antibodies and lower mortality rates for hospitalized patients with COVID-19 who are not on ventilators. The findings, “Convalescent Plasma Antibody Levels and the Risk of Death from Covid-19,” appear today in the New England Journal of Medicine.

This was a pre-planned analysis of treatment and outcome data on 3,082 patients based on mortality 30 days after receiving one dose of plasma. The plasma doses were assessed as having low, medium and high anti-SARS-CoV-2 antibodies. The data were collected over three months from patients enrolled up to July 4, 2020, as part of the national Expanded Access Program for Convalescent Plasma.

The amount of antibody in the treatments was not known at the time of treatment and was determined later. The group of patients receiving the plasma with low antibody levels had the highest mortality rate at 29.6%. Mortality for those receiving the medium-level antibody convalescent plasma was 27.4%. High antibody convalescent plasma showed the lowest mortality rate, 22.3%. The study also showed a more positive outcome for patients who received the plasma within three days of hospitalization. There was no effect on mortality for patients who were on mechanical ventilators.

Patients selected to receive convalescent plasma were 18 years and older, hospitalized with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), and had or were progressing to severe or life-threatening COVID-19. The cohort of patients came from 680 acute-care facilities across the country. The cohort consisted of 61% men and 39% women. Cohort members were 47% white, 37% Hispanic, and 23% Black; and 69% were under age 70. Of the total cohort of 3,082 patients, 2,014 were not undergoing ventilation before convalescent plasma transfusion.

The researchers note that the outcome findings were limited by low numbers with antibody data, abbreviated data collection forms, imprecise details of the relationship between other medication use and the plasma transfusion, and missing data due to the nature of a national registry. They also say the interpretation of the data is limited by the open-label design of the study ― that is, there is limited instruction or control over administration ― and the lack of the design as a traditional randomized clinical trial.

This project has been funded in part with federal funds from the Biomedical Advanced Research and Development Authority, part of the Office of the Assistant Secretary for Preparedness and Response of the U.S. Department of Health and Human Services, under Contract No. 75A50120C00096. Additionally, this study was supported in part by National Center for Advancing Translational Sciences (NCATS) grant UL1TR002377; National Heart, Lung and Blood Institute (NHLBI) grant 5R35HL139854; National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) 5T32DK07352; Natural Sciences and Engineering Research Council of Canada (NSERC) PDF-532926-2019; National Institute of Allergy and Infectious Disease (NIAID) grants R21 AI145356, R21 AI152318 and R21 AI154927; R01 AI152078 9; National Heart Lung and Blood Institute RO1 HL059842; National Institute of Aging (NIA) U54AG044170; Eric and Wendy Schmidt; United Health Group, National Basketball Association (NBA); Millennium Pharmaceuticals, Octapharma USA Inc.; and the Mayo Clinic.


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Media contact: Bob Nellis, Mayo Clinic Public Affairs, 507-284 5005,


Information in this post was accurate at the time of its posting. Due to the fluid nature of the COVID-19 pandemic, scientific understanding, along with guidelines and recommendations, may have changed since the original publication date

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