Baltimore, MD—Administering convalescent plasma within 9 days after onset of COVID-19 symptoms reduced the risk of disease progression leading to hospitalization in mostly unvaccinated patients, according to a study.

The effectiveness of polyclonal convalescent plasma, which can be obtained from donors who have recovered from COVID-19, has been uncertain when it comes to preventing serious complications in outpatients with recent symptoms, according to Johns Hopkins School of Medicine–led researchers.

For the multicenter, double-blind, randomized, controlled trial described in a New England Journal of Medicine article, the study team evaluated the efficacy and safety of COVID-19 convalescent plasma compared with control plasma. Participants—symptomatic adults who had tested positive for severe acute respiratory syndrome coronavirus 2 (SARS-COV-2) without regard for their risk factors for disease progression or vaccination status—were enrolled from June 3, 2020, through October 1, 2021.

Of those who were enrolled within 8 days after symptom onset, 1,181 received a transfusion within 1 day after randomization. Defined as the primary outcome was COVID-19–related hospitalization within 28 days after transfusion. Researchers in this study, Convalescent Plasma to Limit SARS-CoV-2 Associated Complications (CSSC-004), used a transfusion of COVID-19 convalescent plasma containing >1:320 SARS-CoV-2 antispike protein antibody levels.

Including only participants who received a transfusion, the primary outcome occurred in 17 of 592 participants (2.9%) who received convalescent plasma compared with 37 of 589 participants (6.3%) who received control plasma (absolute risk reduction, 3.4 percentage points; 95% CI, 1.0-5.8; P = .005). That corresponded to a relative risk reduction of 54%.

"Evidence of efficacy in vaccinated participants cannot be inferred from these data because 53 of the 54 participants with COVID-19 who were hospitalized were unvaccinated and 1 participant was partially vaccinated," according to the authors. "A total of 16 grade 3 or 4 adverse events (7 in the convalescent-plasma group and 9 in the control-plasma group) occurred in participants who were not hospitalized."

Background information in the article noted, "In the United States, approximately 8% of persons are hospitalized after infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which causes coronavirus disease 2019 (COVID-19). Most therapies for COVID-19 have targeted disease progression or death in hospitalized patients. However, the FDA issued an emergency use authorization (EUA) for three monoclonal-antibody therapies for outpatients after data showed decreases in the incidences of disease progression and hospitalization when these therapies were administered within 5 to 7 days after the onset of COVID-19. Alternative outpatient therapies are needed, particularly in settings where monoclonal-antibody therapy is either unavailable (e.g., in low-income and middle-income countries), scarce, or ineffective (i.e., because of monoclonal antibody–resistant variants)."

The authors advised that safety concerns about COVID-19 convalescent plasma have not been identified in hospitalized populations. They added that, while one study showed that high-titer COVID-19 convalescent plasma administered soon after hospitalization reduced the incidence of death from that infection by half, other data from randomized clinical trials have not shown consistent benefit in hospitalized patients.

In general, however, improved outcomes are associated with the provision of high-titer plasma within days after the onset of symptoms, according to the researchers.

Less data exists involving COVID-19 outpatients, according to the report. Data from randomized trials involving outpatients with COVID-19 are limited. Some have demonstrated significant risk reduction in progression to severe disease, but one study looking at administering the plasma to emergency department patients at high risk for progression to COVID-19 was stopped due to futility, it noted.

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