Red Cross website. “Convalescent plasma is the liquid part of blood that is collected from patients who have recovered from an infection,” according to the FDA.RELATED: Researchers wonder if survivor plasma could prevent coronavirus AdvertisementWhile it is not proven that the plasma is an effective treatment for COVID-19, it does allow most patients to have plasma transfusions without the risk of suffering an allergic reaction and other side effects, according to the FDA.“Among patients with severe or life-threatening COVID-19, convalescent plasma therapy added to standard treatment did not significantly improve the time to clinical improvement within 28 days, although the trial was terminated early and may have been underpowered to detect.