Question: I know that convalescent plasma can be beneficial treatment for some COVID cases.  With far more of us vaccinated, can plasma from vaccinated people serve the same purpose?

Answer: When it comes to using plasma for treatment, the FDA’s Guidelines on Investigational COVID-19 Convalescent Plasma preclude use of plasma from vaccinated individuals who never contracted COVID.  The FDA has several other eligibility criteria, including that the donor’s symptoms must be completely resolved for at least 14 days before donation and the plasma must have high concentration of SARS-specific antibodies. An estimate from one US-based donation center suggests that only 19.5% of plasma donations meet the FDA’s high antibody concentration criteria (see editorial published in NEJM). The reason for the focus on previous infection rather than vaccination is that plasma from previously infected individuals contains antibodies directly related to their immune response to SARS-CoV-2 infection; these types of antibodies are preferable for treatment purposes. 

Regardless, evidence on the effectiveness of blood plasma for treatment is mixed. The largest meta-analysis to data concluded that “Among patients with COVID-19, treatment with convalescent plasma compared with control was not associated with improved survival or other positive clinical outcomes.” (see study published in JAMA). A more recent study suggested that the benefit was greatest when plasma transfusions had high levels of antibodies and were given at early stages of disease (see study from NEJM).  Several researchers suggest that “antibody-rich convalescent plasma from previously infected patients vaccinated with at least one dose of the BNT162b2 vaccine might be more effective than the convalescent plasma from non-vaccinated patients” (see recent comment from Lancet), and the FDA suggests that such a hypothesis be tested in the context of a clinical trial.