An experimental treatment halved hospitalizations for COVID-19, but don’t expect it to reach U.S. pharmacies anytime soon.

The medicine is a single injection of interferon lambda, a version of a natural human molecule that amplifies antiviral action in the respiratory tract.

In a study of nearly 2,000 people in Brazil and Canada, the medication reduced the need for hospitalization in vaccinated and unvaccinated individuals, during both the delta and omicron waves. The findings were published in The New England Journal of Medicine.

Because it activates the body’s own immune system, interferon lambda should work on any variant, or any respiratory virus.

The coronavirus would be unlikely to evolve resistance to the treatment.

Most patients in the study were at high risk from COVID, due to age or other medical conditions. Providing the injection within a week of symptom onset in vaccinated people reduced the rate at which participants needed hospitalization or a lengthy emergency department visit.

The medication was even more successful if given within three days of symptoms starting, or to unvaccinated individuals.

The rate of side effects was similar between patients who received the interferon or a placebo, indicating it’s a safe treatment.

New COVID treatment options are sorely needed. Paxlovid is currently underutilized. Antibody treatments are no longer authorized because they aren’t a good match for currently circulating strains.

And some experts are worried that molnupiravir, already a less-used option, is causing the coronavirus to mutate in dangerous ways, reports Ewen Callaway at Nature.

But interferon lambda faces regulatory hurdles, executives from manufacturer Eiger Pharmaceuticals told Mueller. The trial was conducted outside the United States, where the FDA prefers to see results originate.

The FDA told Eiger late last year that it was not ready to grant lambda interferon emergency authorization. The company may pursue authorization in other nations, such as China, Mueller reports.

The interferon lambda data, which have been available for almost a year, “look quite promising,” according to Dr. Paul Sax of Brigham and Women’s Hospital.