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Convalescent plasma treatment of severe COVID-19: A matched control study

Our take —

In this small, single-center study posted as a non-peer-reviewed preprint, use of convalescent plasma was associated with improved survival and reduced supplemental oxygen demands when compared to retrospectively-collected propensity-matched controls. Because this study lacked randomization and thus there may have been unobserved differences in baseline characteristics between the plasma and comparison groups, data that take advantage of random assignment of convalescent plasma, or a strong non-experimental study design, are needed to verify the findings.

Study design

Retrospective Cohort

Study population and setting

This study included 45 hospitalized COVID-19 patients from an academic medical center in New York City who were enrolled into the study between March 24 and April 8, 2020. Inclusion criteria were defined by eligibility for SARS-CoV-2 convalescent plasma under FDA emergency investigation new drug criteria (eIND). 39 of 45 eligible patients were transfused with convalescent plasma from COVID-19 patients with anti-spike antibody titers greater than or equal to 1:320. Comparison patients with similar baseline demographic and clinical characteristics were selected retrospectively from the medical records system through propensity score matching, selecting four matched comparison subjects for each transfused patient.

Summary of Main Findings

By day 14, there was no significant difference in clinical condition between plasma patients and controls (p=0.167), however, the adjusted odds ratio for worsening oxygenation was 0.86 (95% CI: 0.75-0.98, p=0.028), showing some benefit of plasma transfusion. Additionally, patients receiving convalescent plasma had increased survival when compared to controls (log-rank test: p=0.039). In an adjusted model, use of convalescent plasma was associated with improved survival in non-intubated patients (adjusted OR 0.19; 95% CI: 0.05-0.72; p=0.015) but this effect was not observed in intubated patients (adjusted OR 1.24; 95% CI: 0.33-4.67; p=0.752)

Study Strengths

There was some control of baseline confounding factors using propensity scores and exact matching.


The sample size of the study was small. The study recruited patients from a single academic hospital center in an urban location, limiting generalizability of findings. Receipt of convalescent plasma was not assigned randomly, raising concerns about observed and unobserved differences in baseline factors between groups. Matching controlled for some observed characteristics but it is unknown what other unobserved factors may have related to receipt of plasma and outcomes and thus potentially biased the study results.

Value added

This is the largest study of convalescent plasma to date and warrants further investigation with prospective randomized controlled trials.