Several clinical trials are examining the use of so-called convalescent plasma for COVID-19, but none have been completed and results aren’t expected for at least several more weeks.

Some of the studies are struggling to attract participants because of programs that give patients a more certain path to the therapy and a way to avoid the risk of ending up with a placebo in a clinical trial. Researchers fear that Sunday’s decision by the Food and Drug Administration to issue an emergency waiver will make it harder to get patients into clinical trials and get a more definitive picture on whether and how convalescent plasma actually works to treat COVID-19.

Plasma is the liquid portion of the blood. Convalescent plasma collected from those who have recovered from the coronavirus contains antibodies that some researchers say could help patients who have been newly diagnosed with COVID-19. President Donald Trump has called the therapy “something very special.”

Political Controversy

The emergency-use clearance followed accusations by Trump that U.S. regulators had held off in order to dim his chances of re-election. Some senior U.S. health officials had been reported to have cautioned against issuing a clearance until researchers could collect more data.

Antibodies are one of the main infection-fighting compounds produced by the immune system. They remain in the blood of patients who have recovered from disease, and using them to help another person fight infection is an old idea. Convalescent serum was used to fight the 1918 flu pandemic. The first Nobel Prize in Physiology or Medicine was awarded to Emil von Behring in 1901 for his work studying serum therapy for diphtheria.

However, there are many questions that remain about what convalescent plasma is and who should get it. People sickened by a pathogen produce their own antibodies; sorting out which antibodies actually fought off a disease is a complicated task for researchers. Doctors also want to make sure that introducing foreign antibodies won’t make people sicker.

Expanding Access

The Mayo Clinic is running a program that has helped expand access to convalescent plasma in the pandemic. So far, almost 70,000 people have been infused at more than 2,700 sites around the U.S., according to its website. Data show that patients were 35% less likely to die if they received a high dose of convalescent plasma, compared with those who got lower doses.

All of those enrolled, however, were given the plasma and the antibody levels weren’t checked before it was administered, making it difficult to determine exactly how much benefit patients would get over current care.

The results have been posted online but not yet published in a medical journal, and theydon’t have the same rigor as a clinical trial, which typically compares a treatment to the standard of care. The FDA asked Mayo Clinic for more data, which the clinic said in an e-mailed statement it has shared with agency reviewers.

“We agree on the need for randomized clinical trials as a scientifically sound approach,” the Mayo Clinic said in the statement. Data from the expanded-access program “is significant and could be used to provide evidence” to conduct trials in the future.

Enrollment Issues

National Institutes of Health Director Francis Collins recently held a Zoom meeting with scientists conducting plasma clinical trials, according to Mila Ortigoza, an infectious-disease specialist at New York University who is leading a study on the use of plasma as a treatment in hospitalized patients. She said in an interview that Collins wanted to know how NIH could help. Her team has since been sending NIH enrollment updates daily, and she said she will share data with NIH as it becomes available.

The trial that NYU is conducting with the Albert Einstein College of Medicine recently expanded to three states outside of New York when researchers were only able to enroll 190 patients out of the 300 they’re seeking. Ortigoza said many hospitalized patients want to be guaranteed they will get plasma and choose to go through the Mayo Clinic’s program instead of enrolling. She fears an emergency authorization by the FDA could exacerbate the situation.

“We don’t want to go through another pandemic 100 years from now not knowing if this therapy works,” she said.

Ortigoza hopes her trial will enroll enough people to start producing data on whether convalescent plasma works by the end of September. An effort to pool trial data on hospitalized patients led by NYU could have data sooner, she said.

Data Delay

Two trials by Johns Hopkins University researchers have also had trouble attracting patients to participate, which has pushed back the delivery of results. Researchers there are investigating plasma’s potential to prevent contracting the virus and its ability to help in the early stages of infection.

The studies may produce preliminary data in October, Shmuel Shoham, an expert in oncology infectious diseases who is co-leading the studies, said in an interview.

“Initially, I was thinking we’d have information by now,” he said.

The Johns Hopkins researchers would like to enroll 1,100 people total in the trials but so far have enrolled 60, Shoham said. Recruitment has been difficult at some of the 30 sites around the country. The virus has disproportionately affected Black and Latino people, who often either aren’t sought after or don’t participate in clinical trials.

“I believe that progress happens at the speed of trust,” Shoham said. “We’re trying, in a very compressed timetable, to gain the trust of communities where there is a trust deficit.”