It would seem with dwindling viral cases, millions of vaccines deployed, and an end to a public health emergency that, Covid-19 is finally petering out. On the contrary, the virus is here to stay, much like the seasonal flu. While vaccines have been shown to prevent the majority of severe cases, there’s still only one effective and federally approved therapeutic, called Paxlovid, which has to be taken within five days of symptoms to be effective.

But we may have a new, versatile antiviral to add to the arsenal, according to a study published this week in the New England Journal of Medicine. Derived from a chemical that’s naturally part of the immune system, the drug has been shown to cut down the risk of Covid-19 hospitalization significantly, even for people who are unvaccinated.

What is this new treatment, exactly?

The full name is a bit of a mouthful: pegylated lambda interferon (PEG-lambda for short). Interferons are like chemical Paul Reveres of the immune system. When our immune systems sense an invader, they produce these chemicals to warn other uninfected neighboring cells of the invader. This warning cry allows for the body to rev up the production of anti-viral proteins and other chemicals, effectively creating a bulwark against a viral takeover and signaling to more specialized immune cells, such as T cells, to clear out the infection.

PEG-lambda itself is a synthetic interferon discovered and developed over two decades ago and, so far, has been tested in treating hepatitis infections. In particular, the drug is a special class of interferon called type III interferon that helps the immune system resist viral pathogens predominately in mucosal tissues like the respiratory tract.

This local action is what makes PEG-lambda so attractive (also the fact that it doesn’t directly interact with Covid-19, so there is less chance of the virus mutating to evade it). Too much interferon can put the immune system in overdrive, which can lead to harmful side effects like persistent inflammation (which isn’t good). But having a drug that acts where coronavirus tends to first settle down and replicate in the respiratory tract means you can boost the body’s interferon response with minimal side effects.

Does it work against Covid-19?

In clinical trials conducted in Canada and Brazil, over 930 people given the PEG-lambda shot were compared against over 1,000 people who received a placebo. Most participants involved were relatively at a high risk of Covid-19 infection because of their age (being 50 years or older) or due to underlying medical conditions or a weakened immune system. The researchers found that only 25 out of the 931 patients in the interferon group (around 2.7 percent) had to be hospitalized, compared to 57 out of the 1,018 in the placebo group (or 5.6 percent).

The researchers also found that if the drug was given within seven days of a patient showing Covid-19 symptoms, they were 51 percent less likely to be hospitalized or go to the emergency room. The odds improved to 58 percent if PEG-lambda was given within three days.

The shot seemed to be pretty effective for folks who weren’t vaccinated. Among the 17 percent of clinical trial participants who weren’t vaccinated, those who received the shot within three days of showing symptoms were a whopping 89 percent less likely to be hospitalized. Multiple different Covid-19 variants emerged during the course of the trial, and the drug seemed most potent against the Omicron strain.

Another icing on the cake was the lack of significant side effects, with those who got PEG-lambda suffering no worse than those who got the placebo.

When can we expect it?

That’s still unknown. While Eiger Pharmaceuticals, who created the drug, applied to the U.S. Food and Drug Administration for emergency use authorization, the agency did not grant it under the grounds the clinical trials did not include a U.S. site and that the study was run by academic researchers and not the company itself, The New York Times reported.

Pending further clinical trials to meet the FDA’s approval, PEG-lambda may become an available treatment option in Australia or China as Eiger executives consider seeking authorization in those countries. But if PEG-lambda does manage to snag federal approval down the road, emergency basis or not, it ultimately could be a tool in preventing and treating other viruses like the seasonal flu or outbreaks of the respiratory syncytial virus. Only time, and further research, will tell.