An approved antibody cocktail reduces mortality by a full 20% in COVID-19 patients who cannot naturally mount an immune response to the disease, a large new trial has found. 

The results suggest that clinicians will have a clearer path for treating patients with acute disease, observers say.

The drug, REGEN-COV, made by Regeneron Pharmaceuticals, includes two monoclonal antibodies that bind to the coronavirus spike protein and neutralize the virus. Delivered via intravenous infusion, it already has been shown to halt disease progression in sick COVD-19 patients who are not hospitalized. It also has been shown to prevent the disease altogether at a lower dose in healthy people. The latest trial is the first study large enough to confirm that the treatment reduces mortality in patients hospitalized with severe COVID-19, according to researchers at the University of Oxford, Oxford, U.K.

Between Sept. 18, 2020, and May 22, 2021, more than 9,700 patients hospitalized with COVID-19 were randomly allocated to receive usual care plus the antibody treatment, or usual care alone, as part of the RECOVERY drug trial. 

About one third of the patients were seronegative, meaning that they were not able to mount a response to the virus and were at great risk of serious outcomes. In fact, seronegative patients who received usual care alone were twice as likely to die within 28 days than patients who did produce antibodies to the disease. But for seronegative patients who received the antibody cocktail, 28-day mortality was reduced by one-fifth when compared with the usual-care cohort, investigators reported.

Study participants who made their own antibodies to the virus did not benefit from the treatment, however.

The results may ease some of the uncertainty about the value of antiviral therapies in late-stage COVID-19, the researchers said in a statement following release of the findings. 

“We now know that this antibody combination is not only bad for the virus but it is also good for the sickest patients who have failed to mount a natural immune response of their own,” said joint chief investigator Sir Martin Landray, M.D. “That is excellent news. It is the first time that any antiviral treatment has been shown to save lives in hospitalized COVID-19 patients,” he said.

“If [patients] do not have antibodies then treatment with antibody-based drugs to the spike protein can reduce their risk of death and also time spent in hospital,” added the Medical Research Council’s Fiona Watt.

It also is important to know that patients who mount their own antibody defense are not helped by and should not receive the therapy — especially given the costs of drugs, she concluded.