Blood plasma transplants are being used to treat coronavirus patients in the US - here’s how they work

Like blood donations, stocks of convalescent plasma are currently in very limited supply. (Shutterstock)

The United States Food and Drug Association (FDA) has now authorised the use of convalescent plasma to treat Covid-19 patients.

The news was announced by the FDA on Sunday 23 August, after Donald Trump criticised health officials for moving too slowly in making the decision last week.

However, the move is a contentious one, criticised by both FDA health officials and medical professionals.

So how exactly is convalescent plasma used, and is it effective when it comes to fighting coronavirus?

What is convalescent plasma?

The NHS website describes standard blood plasma as a “yellowish liquid that makes up about half your blood volume.” However, convalescent plasma specifically is slightly different.

Once someone has contracted coronavirus, their blood plasma will contain antibodies which their body will use to help them fight further infection. Convalescent plasma is the name for this antibody-rich plasma.

At the end of March, the FDA set up a convalescent plasma trial, studying its impacts on coronavirus patients. Since then, it has been used to treat over 60,000 Covid-19 patients.

How blood plasma transplants work

Convalescent plasma is taken from the blood of people who have recovered from Covid-19. This antibody-rich plasma is then transfused into patients whose immune systems are not developing enough of their own antibodies in order to fight the virus.

However, like blood donations, stocks of convalescent plasma are currently in very limited supply and require many donors to come forward to replenish them.

What claims have been made about the treatment?

At a White House briefing, Alex Azar (US Health and Human Services Secretary) explained that studies with 70,000 participants had justified the FDA’s Emergency Use Authorization (EUA) of blood plasma transplants.

However, Azar appeared to be referring to a national study which involved just 35,000 patients who were treated with convalescent plasma.

He said at the briefing, “The data we gathered suggests that patients who were treated early in their disease course, within three days of being diagnosed, with plasma containing high levels of antibodies, benefited the most from treatment.

“We saw about a 35 per cent better survival in the patients who benefited most from the treatment.”

The study appeared on August 12 in a pre-print, rather than a peer-reviewed scholarly or scientific journal. It claimed that about 12 per cent of patients who were treated in the later stages of their disease (four days or more after their diagnosis) had died, whereas only 8.7 per cent of patients who were treated quickly (within three days of diagnosis) had a fatal outcome.

Additionally, the chance of patients who received plasma containing the highest amounts of antibodies dying within a week of treatment was 35 per cent lower, compared to those treated with less antibody-rich plasma.

In order to test the validity of the treatment, comparisons in medical trials are normally made between treated patients and completely untreated patients, rather than comparisons being made between the dates a patient is treated.

Doctors usually measure the benefit of a treatment using a variable-controlled clinical trial in which they randomly select which patients receive treatment and which ones do not, in order to rule out other influences affecting the final results, such as placebo.

Who has criticised the validity of the findings?

Announcing the news on Sunday, the US Food and Drug Administration claimed that the “known and potential benefits of the product outweigh the known and potential risks of the product.”

However, some do not agree with this claim, and argue that more data is required to come to such a conclusion.

The lack of a randomised clinical trial on convalescent plasma for the treatment of Covid-19 is a main concern among critics.

Following the FDA’s announcement on Sunday, Dr Jonathan Reiner, a professor of medicine at George Washington University and a CNN medical analyst criticised the decision, explaining, “The problem is, we don't really have enough data to really understand how effective convalescent plasma is.”

Meanwhile, Dr Thomas File, the president of the Infectious Diseases Society of America, also criticised the lack of data taken into consideration before the decision was made.

He explained in a statement, “While the data to date show some positive signals that convalescent plasma can be helpful in treating individuals with COVID-19, especially if given early in the trajectory of disease, we lack the randomized controlled trial data we need to better understand its utility in COVID-19 treatment.”

Additionally, after the EUA was issued, Eric Topol (founder and director of the Scripps Research Translational Institute) criticised the lack of a peer reviewed study, calling the findings "outrageous."

He took to Twitter to criticise President Trump and the FDA, writing, “Outrageous to listen to @realDonaldTrump @secAzar @SteveFDA claiming a 35 percent improved survival in an observational preprint study compared w/ late-treated patients. There's no evidence to support any survival benefit. 2 days ago FDA's website stated there was no evidence for an EUA.”

Topol suggested that the FDA had caved to pressure from The White House when deciding to issue the EUA.

“There is no breakthrough and the @US_FDA commissioner @SteveFDA has caved to Trump's pressure (including yesterday's tweet) to promote it as if there was one,” he tweeted.

Is the NHS using blood plasma transplants?

Currently 181 hospitals in the UK are taking part in a nationwide clinical trial, run by the NHS, to determine if blood plasma transplants can help in the national effort against the virus.

Earlier this month, the NHS Blood and Transplant department made an urgent appeal for more blood plasma donors to come forward and take part in the trial. It is still urging both men and women over the age of 17, who have recovered from coronavirus to donate their antibody-rich blood plasma.

However, as trials are still underway the NHS has not yet come to a conclusion on its effectiveness as a treatment.

You can apply to take part in the trial here.