Convalescent plasma for Covid-19: NIH calls FDA’s evidence “insufficient”

The National Institutes of Health on Tuesday put out a blunt statement on the use of convalescent plasma to treat Covid-19, calling the evidence for its effectiveness “insufficient.”

“There are currently no data from well-controlled, adequately powered randomized clinical trials that demonstrate the efficacy and safety of convalescent plasma for the treatment of Covid-19,” according an NIH treatment guidelines panel that reviewed the evidence. “There are insufficient data to recommend either for or against the use of convalescent plasma for the treatment of COVID-19.”

The statement was clearly aimed at the Food and Drug Administration, which granted a controversial Emergency Use Authorization, or EUA, for convalescent plasma on August 23.

Some researchers saw the approval as a politically motivated decision, given the weak evidence for its effectiveness coupled with President Trump’s public attacks on the FDA. (Trump had alleged without evidence that the agency was slow-walking approvals of Covid-19 treatments to hurt his election prospects.)

The EUA announcement drew criticism almost immediately. Scientists noted that administration officials overstated the evidence showing that convalescent plasma was a viable treatment for Covid-19 during a White House press conference.

“The evidence [the FDA is] drawing on is not ready for primetime,” Jeremy Faust, an attending physician in the Brigham and Women’s Hospital and an instructor at Harvard Medical School, told Vox.

The EUA for convalescent plasma came after many experts, including Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, had warned the agency there wasn’t enough evidence to fast-track authorization for the novel treatment.

However, FDA commissioner Stephen Hahn said in an August 23 statement that he was “encouraged by the early promising data that we’ve seen about convalescent plasma,” adding that “plasma from patients who’ve recovered from Covid-19 has the potential to help treat those who are suffering from the effects of getting this terrible virus.”

President Trump, meanwhile, described the treatment as a “breakthrough.”

But on August 24, Hahn walked back some of his claims on Twitter the day after he made them during a White House press conference.

Convalescent plasma is already being used to treat dire cases of Covid-19 and is being studied by several research groups. But there is currently no Covid-19 treatment that has received full FDA approval.

For many scientists and watchdog groups, the central concern is that the FDA is once again yielding to political pressure. The agency rushed an EUA in March for the anti-malaria drug hydroxychloroquine after President Trump repeatedly touted the drug as a “game changer” despite flimsy evidence for its effectiveness. The EUA was then revoked in June after the agency said the drug was “unlikely to be effective” and could cause serious side effects like heart arrhythmias.

In a Twitter thread, Hahn pushed back, saying that the decision to greenlight convalescent plasma was made based on the data, not political considerations.

But the new NIH statement undercuts these claims, noting that in addition to weak evidence for its effectiveness, there is also an alarming lack of information on the long-term risks of using convalescent plasma.

With more than 185,000 people across the United States dead from Covid-19, there’s an urgent need to find good treatments. And as the November election approaches, President Trump is desperate for good news. However, even the appearance of political pressure could undermine confidence in government agencies and their backing for other treatments and vaccines, adding to the long list of public health missteps and confusion around the pandemic.

The FDA is playing up weak evidence to justify its EUA for convalescent plasma

Plasma is the liquid part of the blood that includes proteins used for clotting (as opposed to serum, which is the liquid part of blood leftover after blood clots). With convalescent plasma therapy, doctors harvest plasma from people who have recovered from Covid-19 and transfuse it to people who are currently suffering from an infection.

The idea is that the plasma from people who have successfully withstood the virus contains antibodies, which can interfere with how a pathogen works or mark it as a target for elimination. This passive immunity can then keep the disease in check or help the recipient’s immune system eradicate it. It’s an approach that’s been around for more than a century and used with varying degrees of success for other coronaviruses like SARS and MERS.

But Covid-19 is a markedly different disease, and so far, no randomized control trials — the gold standard of evidence — on convalescent plasma have been completed.

The FDA memo outlining the EUA for convalescent plasma cites just two randomized controlled trials, both of which were stopped early — one because it failed to recruit enough participants and the other because they found that the patients that were receiving plasma already had high levels of antibodies. Both found little to no benefit from the treatment, but they remain some of the best-constructed studies.

The memo also cites a handful of observational and retrospective studies as the basis for its decision. It was one of these retrospective studies that served as the basis for the White House’s boldest claim about the effectiveness of convalescent plasma to treat Covid-19.

During the August 23 press conference, Hahn reported that convalescent plasma would yield a 35 percent improvement in the survival rate of Covid-19 patients.

“A 35 percent improvement in survival is a pretty substantial clinical benefit,” said Hahn during a Sunday press conference. “What that means is, if the data continue to pan out, if 100 people are sick with Covid-19, 35 would have been saved with the administration of plasma.”

But other researchers said that Hahn’s 35 percent improvement in survival claim was wildly misleading. It came from a retrospective preprint study that hasn’t undergone peer review, so some of the methods and findings may have flaws that would ordinarily be caught in the review process.

“For the first time ever, I feel like official people in communications and people at the FDA grossly misrepresented data about a therapy,” Walid Gellad, of the Center for Pharmaceutical Policy and Prescribing at the University of Pittsburgh, told the New York Times.

The study doesn’t compare patients who received convalescent plasma to patients who received a placebo, either. Rather, it compares patients who received plasma early versus those who received it later in their course of treatment.

Even within that comparison, the results showed that the seven-day mortality rate was 11.9 percent in patients who received plasma four days or more after they were diagnosed with Covid-19, while those who received plasma three days after diagnosis had a mortality rate of 8.7 percent. In other words, getting plasma to Covid-19 patients one day earlier reduced the absolute mortality by 3.2 percent.

And when the researchers compared the doses of convalescent plasma, they found that those that received the low dose had a seven-day mortality rate of 13.7 percent while those that received the high dose had a rate of 8.9 percent. That’s a only 4.8 percent improvement in absolute terms, but a 35 percent change in relative terms. It’s progress, but not the massive leap forward that Hahn and other officials made it sound like.

Faust pointed out that this retrospective study only sampled patients who were sick enough to go to the hospital. Out of those, the patients studied were only the ones who received convalescent plasma, were under the age of 80, and who did not receive mechanical ventilation.

“This big ‘breakthrough’ that they say is a 35 percent reduction in mortality, this is a subset of a subset of a subset in a retrospective study which has not been confirmed with a trial,” he said. “There’s nothing wrong with the study itself for what it is; what’s wrong is to rely on it to say that there’s been a breakthrough.”

On August 24, Hahn acknowledged, after much criticism, that he overplayed his hand. “What I should have said better is that the data show a relative risk reduction not an absolute risk reduction,” he wrote.

But for some researchers, it was not enough. A few responded on Twitter that they wanted a more forceful retraction of the claim and other statements Hahn made during the press conference.

Let’s be clear: Convalescent plasma could be a viable treatment for Covid-19. However, the vast majority of people infected with the virus get better on their own. Determining whether a treatment can actually hasten recovery from the illness requires controlled clinical trials. This means randomly sorting people into two groups — one that receives the treatment and one that receives a placebo — and then monitoring their progress with the disease. Such data is still lacking for convalescent plasma.

And the FDA’s EUA may have made it harder to study the treatment, making ongoing clinical trials more difficult. It becomes harder to recruit patients into clinical trials for convalescent plasma where they may receive a placebo if they know that they could get the actual treatment from their doctor.

This treatment also carries risks. Plasma transfusions can lead to complications like acute lung injury and severe allergic reactions leading to anaphylactic shock. The NIH also raised the concern that convalescent plasma could weaken the recipient’s own immune response to Covid-19, making the patient vulnerable to reinfection. These are not common outcomes, but the risk isn’t zero. For people who are sick with Covid-19, it may be worth accepting some of these risks if there is a clear benefit. But if there isn’t, it becomes much harder to tolerate.

“You’re essentially asking people to play roulette with a treatment that may not work,” Faust said.

All this means that it’s crucial to establish that convalescent plasma carries benefits that outweigh its risks before clearing it for widespread use.

The FDA is undermining its own credibility at a critical time

National and international health agencies have made a number of missteps during the Covid-19 pandemic, from how the World Health Organization reversed course on whether the virus could be spread person to person to the back and forth in the US about wearing masks.

But the political pressure mounting on the FDA from the White House could end up being the most consequential erosion of credibility since it could undermine the public’s trust in treatments for Covid-19 as well as an eventual vaccine.

President Trump has made no secret of his view that a treatment or vaccine for Covid-19 is critical to his election hopes, and he has blamed the FDA for undermining him.

And White House Chief of Staff Mark Meadows made it clear that pressuring the FDA to approve drugs and vaccines ahead of the election is part of Trump’s strategy. “If they don’t see the light, they need to feel the heat because the American people are suffering,” he told ABC on August 23. “This president knows it, and he’s going to put it on wherever — the FDA or NIH or anybody else — to make sure that we deliver on behalf of the American people.”

With the perception that drugs are being issued to meet the president’s demands, patients may be reluctant to take them.

That’s why some health advocates are so distressed by the FDA’s authorization of convalescent plasma, which serves as yet another example of politics getting its way over science.

“Make no mistake, the FDA’s decision to grant an emergency use authorization for COVID-19 convalescent plasma on the eve of the Republican National Convention represents the most blatant politicization of FDA decision-making in history,” said Michael Carome, director of the Health Research Group at the watchdog group Public Citizen, in a statement. “Such action seriously damages the FDA’s credibility during the greatest public health crisis in 100 years.”

And if a vaccine for Covid-19 were to get an EUA before the November election — before phase 3 trials are complete — there will be concerns that it too was rushed. Fewer people might be inclined to get vaccinated, out of safety fears, making it harder to control the disease. That will have tremendous impacts on the lives of millions of people as they cope with the continued spread of the virus.

Building trust in public health agencies is therefore essential for ending the Covid-19 pandemic, but it will take time. Hyping weak results or unproven drugs undermines this fragile confidence.

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