The FDA’s decision to grant Emergency Use Authorization (EUA) for convalescent plasma in patients with COVID-19 has led many investigators to voice concerns that not enough patients with the infection will enroll in randomized controlled trials of the therapy going forward.

An FDA memo justified the decision to grant an EUA to convalescent plasma based on data from a limited number of controlled and uncontrolled trials as
well as data from a Mayo Clinic open-label, expanded access program. Around 15 out of 54 randomized controlled trials studying convalescent plasma for COVID-19 are currently under way in
the U.S.

Investigators are citing worries that patients with the disease, especially those who are hospitalized or severely ill, may choose not to enlist in these trials for fear of receiving a placebo. Now that the EUA is in place, these patients may instead opt to receive plasma. Investigators are concerned that this will lead to a lack of sufficient efficacy and safety data for the therapy in patients with COVID-19.

A convalescent plasma study conducted at Montefiore Medical Center in New York and four other sites, for instance, has enrolled only 190 patients since late April. This number is far lower than the 300-patient goal for the trial.

Another COVID-19 plasma trial conducted at 30 sites in the U.S and one site at the Navajo Nation has only recruited 25 volunteers out of a goal of 500 participants, according to the trial’s leading investigators at Johns Hopkins University School of Medicine. A similar plasma study from Hopkins conducted at the same 31 sites has only enrolled 50 out of a hoped-for 600 participants.

Shifts in the prevalence of COVID-19 cases in regions where these studies are being conducted may also be contributing to difficulties in enrolling participants with COVID-19, as dwindling cases have resulted in fewer plasma donors for the trials.