At the start of the pandemic, scientists thought that “convalescent plasma” might be a way to treat COVID-19.
By giving patients plasma from people who had recovered (or were cured) of COVID-19, the idea was that this antibody-rich infusion would help their immune systems fight off the infection. This is a tried-and-tested strategy for other infectious diseases, including Ebola, with varying levels of success.
But mounting evidence, including an international study published this week, suggests that convalescent plasma does not save the lives of people seriously ill with COVID-19. The researchers concluded that the therapy was “futile.”
Read more: Coronavirus: What is plasma therapy?
What is convalescent plasma?
Convalescent plasma is a blood product that contains antibodies against an infectious pathogen (such as SARS-CoV-2, the coronavirus that causes COVID-19). It comes from the blood of people who have recovered from an infectious disease.
Scientists use a process called apheresis to separate the different blood components. Red and white cells, and platelets are removed except for plasma, which is rich in antibodies.
The story of convalescent plasma therapy (or serum therapy) begins in the 1890s. This is when physician Emil von Behring infected horses with the bacteria that causes diphtheria.
Once the horses were cured, Behring collected their antibody-rich blood to treat the disease as with humans. This led to him being awarded the first Nobel Prize in Physiology or Medicine in 1901.
Why has convalescent plasma been used to treat COVID?
Convalescent plasma has been used to treat infectious diseases for more than a century. These include: scarlet fever, pneumonia, tetanus, diphtheria, mumps and chickenpox.
Recently, convalescent plasma has been investigated as a treatment for SARS (Severe Acute Respiratory Syndrome), MERS (Middle East Respiratory Syndrome) and Ebola.
At the start of the pandemic, researchers hoped that convalescent plasma could also be used to treat COVID-19.
Read more: I’m a lung doctor testing the blood plasma of COVID-19 survivors to treat the sick – a century-old idea that could be a fast-track to a cure
Preliminary studies and some clinical trials were promising. This led to the widespread use of convalescent plasma for patients with COVID-19 in the United States, a decision supported by the Food and Drug Administration.
As of May this year, more than 100 clinical trials were conducted in people with COVID-19 with convalescent plasma; About one-third of these studies were terminated or discontinued early.
Earlier this year, the results of the United Kingdom’s historic RECOVERY trial were reported. It investigated convalescent plasma therapy (compared to usual supportive care) in more than 10,000 people hospitalized with COVID-19.
Treatment did not reduce the risk of death (24% in both groups), no difference in the number of patients who were cured (66% discharged from hospital in both groups) or those who worsened (29% had shortness of breath). Mechanical ventilation was required to help take both groups).
So for people hospitalized with COVID-19, the researchers concluded that convalescent plasma provided no benefit.
A Cochrane review, which was updated in May of this year and evaluated all available trials, confirmed these results. These trials involved more than 40,000 people with moderate to severe COVID-19 who had received convalescent plasma.
The review found that treatment had no effect on the risk of dying from COVID-19, did not reduce the risk of hospitalization or the need for ventilators to assist with breathing, compared with placebo or standard care. reduced.
In Australia, the National COVID-19 Clinical Evidence Taskforce does not recommend the use of convalescent plasma in people with COVID-19 unless it is in a clinical trial.
Read more: Here’s what happens when you’re hospitalized with COVID
What’s the latest news?
Trial results reported this week come from a major clinical trial involving nearly 2,000 hospitalized patients with moderate to severe COVID-19.
Patients were randomized to receive convalescent plasma or usual care. All patients had other adjuvant drugs used in people hospitalized critically ill with COVID, such as dexamethasone and remdesivir.
The international team of investigators included people from Australia, Canada, the UK and the US.
Although the results and detailed analysis were published this week, the trial was halted in January. This is after the trial committee reviewed the interim results and reported that “convalescent plasma was unlikely to be of benefit to patients with COVID-19 who require organ support in the intensive care unit”. Therefore, the continuation of the trial was considered futile.
Convalescent plasma treatment did not reduce the risk of hospital death in the month following treatment (37.3% convalescent plasma treatment, 38.4% usual care, not treated with convalescent plasma). The median number of days without the need for organ support (such as a mechanical ventilator or cardiac support) in both groups was 14 days. Serious adverse events were reported in 3.0% of people treated with convalescent plasma and only 1.3% of those in the usual care group.
Taken together, the weight of the evidence now clearly demonstrates that convalescent plasma is not a treatment option for people with mild, moderate or even severe COVID-19.
Where next for COVID-19 treatment?
While vaccination is the key strategy to prevent COVID-19, attention is now being paid to some emerging and promising treatments to prevent COVID-19 from getting worse.
These include emerging antiviral treatments that may be used early in the disease, including monoclonal antibodies such as sotrovimab and AZD7442. Then there are potential oral antiviral drugs, such as mollupiravir and PF-07321332.
Read more: Take-at-home COVID drug mollupiravir may be on its way – but vaccination is still our first line of defense