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Convalescent plasma did not reduce Covid-19 deaths or keep patients from severe illness in new study

Posted October 22, 2020 7:40 p.m. EDT

— In a new study, convalescent plasma did not reduce deaths among Covid-19 patients or prevent moderate disease from becoming severe.

The study, conducted in India and published in the medical journal the BMJ on Thursday, suggests that "as a potential treatment for patients with moderate Covid-19, convalescent plasma showed limited effectiveness."

Convalescent plasma is the antibody-rich serum taken from the blood of people who recovered from Covid-19. The idea is that the plasma can help the immune response of patients still fighting the disease.

In August, the US Food and Drug Administration authorized the emergency use of convalescent plasma as a treatment option for hospitalized Covid-19 patients. However, data were still being collected in randomized controlled trials -- the gold standard -- to study the safety and effectiveness of the treatment. Last month, a National Institutes of Health panel said there's no evidence backing the use of convalescent plasma to treat coronavirus patients and that doctors should not treat it as a standard of care until more study has been done.

Randomized controlled trials of convalescent plasma to treat Covid-19 patients are still underway in the United States.

The new study, called the PLACID trial, included data on 464 adults with moderate Covid-19 in 39 hospitals across India. Among them, 235 patients were randomly selected to receive convalescent plasma along with standard care for treatment and 229 patients received only standard care.

The new study showed that a higher proportion of patients who received convalescent plasma saw improvements in their symptoms of fatigue and shortness of breath compared with those given standard care, but there was no difference between patients when it came to resolving fever and cough.

The proportion of patients who needed invasive ventilation did not differ among the two groups, and overall, the researchers found that 34 patients who received convalescent plasma, or 15%, had died -- compared with 31 who were given standard care, or 14%.

The study had some limitations, including that it was an "open label design" so the physicians treating the patients knew who was given convalescent plasma and who wasn't. Additionally, more research is needed to determine whether similar findings would emerge among a larger group of patients in other parts of the world.

Simon Clarke, an associate professor in cellular microbiology at the University of Reading in the United Kingdom, called the new study "a blow" to the use of convalescent plasma as a Covid-19 treatment.

"While this is a blow to the use of plasma therapy for Covid-19, it should not be abandoned, there may be ways to refine it as a treatment and deliver solid, demonstrable benefits," Clarke said in a written statement distributed by the UK-based Science Media Centre.

"Use of someone's blood plasma that contains antibodies against a virus or bacteria to treat an infection in someone else, is not a new technology and although usually safe, is not entirely without risk," said Clarke, who was not involved in the new study.

"The PLACID trial was able to show a small effect on the rate at which patients were able rid themselves of the virus, but this was not enough to improve their recovery from the disease," he added. "In simple terms, there were no clinical benefits to the patients."

Martin Landray, a professor of medicine and epidemiology at the University of Oxford, noted that convalescent plasma is "quite literally, a mixed bag." Some donors in the new study had lower levels of key antibodies, which may mean the therapy wouldn't be as effective.

And while this is the largest randomized trial of convalescent plasma to complete so far, Landray said, it's still too small to give clear answers. Landray co-leads a large Covid-19 treatment trial, the Recovery Trial, which is also studying convalescent plasma.

Larger trials are needed for clear results, he said in a statement, "and even then there would still be questions about whether different types of patient respond better or worse."

"For example, one could well imagine that the treatment might work particularly well in those earlier in the course of the disease or who have not been able to mount a good antibody response to the virus of their own," Landray said. "But such speculation needs to be tested -- we can't just rely on an educated guess."

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