A single injection of Eiger Biopharmaceuticals’ peginterferon Lambda, an immune defense-stimulating protein, cut the rate of COVID-19 hospitalization by 51 percent compared to placebo, researchers reported in the New England Journal of Medicine.

But while the drug was equally effective against both the original SARS CoV-2 strain and three variants, its regulatory future in the U.S. remains in doubt.

Last fall, presented with topline data from the TOGETHER phase 2 study, the FDA declined to hear the company’s application for an Emergency Use Authorization (EUA). The agency suggested that Eiger request an end-of-phase-2 meeting to discuss a company-sponsored pivotal trial that could, eventually, support a biologics license application (BLA).

The phase 2 study was conducted in Brazil and Canada, and while Eiger didn’t pin the rejection on that, the FDA has discouraged submissions based only on international data before.

Interferon Lambda is a naturally occurring protein that the body produces in response to viral attack. According to Eiger, it has been shown to suppress viral replication while stopping cytokine storm, a severe immune reaction.

Eiger is still evaluating the next step for peginterferon Lambda, which it is also developing as a treatment for hepatitis delta infection, a liver disease. But in the NEJM publication, lead author Gilmar Reis of McMaster University in Ontario and colleagues outlined the molecule’s success as a treatment for adults with serious COVID-19 related respiratory infections.

The study comprised 933 patients, most of whom (83 percent) had been vaccinated against the virus. They were randomized to a single subcutaneous injection of peginterferon Lambda 180 micrograms or placebo. The primary outcome was a composite of hospitalization or emergency department admission. Mortality was a key secondary endpoint.

The primary hospitalization endpoint occurred in 2.7 percent of the treated group and 5.6 percent of the placebo group — an absolute 51 percent difference and a relative risk reduction of 49 percent.

The investigators broke response down by viral variant as well. Delta was the most common variant (44 percent), followed by Omicron (40 percent). About 15 percent had a Gamma variant. The remainder were either Alpha, Zeta, or unknown.

The treatment was actually most effective in those with an Omicron variant, reducing the risk of hospitalization by 83 percent. The risk reduction in Delta infections was 46 percent, and in Alpha or Gamma, 26 percent.

So few people died that the mortality endpoint failed to reach statistical significance. Numerically, peginterferon Lambda did appear protective, with one death in the treated group and four in the placebo group.

Read the NEJM paper here: bit.ly/3JUpQ68. — Michele G. Sullivan