(HealthDay News) — COVID-19 convalescent plasma administered to mostly unvaccinated outpatients within 9 days after symptom onset reduced the risk of progression of COVID-19 leading to hospitalization, according to a study published online in the New England Journal of Medicine.

David J. Sullivan, MD, from Johns Hopkins University in Baltimore, and colleagues compared the efficacy and safety of COVID-19 convalescent plasma, as compared with control plasma, in a double-blind, randomized, controlled trial involving symptomatic adults (≥18 years of age) who had tested positive for severe acute respiratory syndrome coronavirus 2. Participants were enrolled within eight days after symptom onset and received a transfusion within one day after randomization. A total of 1181 participants enrolled from June 3, 2020 through Oct. 1, 2021, received a transfusion.

The researchers found that the primary outcome of COVID-19-related hospitalization within 28 days occurred in 2.9% of the 592 participants who received convalescent plasma and in 6.3% of the 589 participants who received control plasma (absolute risk reduction, 3.4%; 95% confidence interval, 1.0 to 5.8; P = 0.005), corresponding to a 54% reduction in relative risk. Since 53 of the 54 participants with COVID-19 who were hospitalized were unvaccinated and one was partially vaccinated, evidence of efficacy in vaccinated participants could not be inferred. Sixteen grade 3 or 4 adverse events occurred in participants who were not hospitalized (seven and nine in the convalescent and control plasma groups, respectively).

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“These recent acknowledgements of high-titer convalescent plasma’s benefit in treating early-stage COVID-19 — in conjunction with our peer-reviewed findings — should encourage clinicians to keep it as a viable therapy option for outpatients,” Sullivan said in a statement.

The study was partially funded by Octapharma.

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