A single-injection antiviral treatment for newly-infected COVID-19 patients reduced the risk of hospitalization by half in a large-scale clinical trial, according to a study published on Wednesday.

Stanford University professor Jeffrey Glenn, coauthor of the study published in the New England Journal of Medicine (NEJM), said the new drug "showed profound benefits for vaccinated and unvaccinated people alike."

While the number of Americans dying daily of coronavirus has fallen to around 500, treatments for the disease remain limited. One of the most common, Paxlovid made by Pfizer, involves taking 30 pills over five days.

The new treatment involves a single dose of pegylated lambda-interferon, a synthetic version of a naturally occurring protein that infected cells secrete to defend against viral infection.

"What it does is it binds receptors on the surfaces of cells that activate our own antiviral defense mechanisms," said Glenn, a professor of medicine, microbiology and immunology who heads the Stanford Biosecurity and Pandemic Preparedness Initiative.

"So if a virus has infected the cell it will turn on processes that aim to destroy the virus's replication," he said. "It will also send signals to neighboring cells to warn them viruses are on their way and get ready to defend yourself."

Receptors for interferon lambda are primarily in the linings of the lungs, airways and intestine — the main places COVID strikes.

"We're turning on these antiviral mechanisms in the cells, the lung, where the infection is happening," Glenn said.

The Phase 3 trial of the drug, conducted between June 2021 and February 2022, involved nearly 2,000 patients with COVID symptoms in Brazil and Canada, about 85% of whom had been vaccinated.

A total of 931 newly-infected COVID patients were given a single injection of interferon lambda while 1,018 participants were given a placebo.

The risk of COVID-19–related hospitalization or death from any cause was 47% lower in the interferon group than in the placebo group, according to the researchers.

Twenty-five of the 931 people who received the injection within seven days of exhibiting COVID symptoms were hospitalized compared with 57 of the 1,018 who received the placebo.

Vaccinated patients treated with interferon lambda experienced a 51% reduction in hospitalization relative to the placebo group.

There was an 89% reduction in hospitalization among unvaccinated patients treated within the first three days of the onset of COVID symptoms compared with the placebo group.

Developed for Hepatitis D 

Glenn said interferon lambda proved effective against all COVID variants tested, including omicron, and side effects in the group receiving the injections were no greater than among the placebo recipients.

Glenn is the founder of a small biotechnology company called Eiger Biopharmaceuticals that acquired interferon lambda to develop drugs for hepatitis delta virus.

"When COVID came, I said this would be the perfect drug for COVID," said Glenn, who left the Palo Alto-based company but remains on the board of directors and is an equity holder.

Eiger sought an emergency use authorization for interferon lambda from the US Federal Drug Administration (FDA) for COVID treatment last year but it was not granted.

That was "very frustrating," Glenn said, but he was hopeful publication of the study in the NEJM "will help encourage regulators here and around the world to find a way to get lambda into patients as soon as possible."