An experimental COVID treatment could be a promising alternative to Paxlovid, study finds

Like other antivirals, Paxlovid is designed to stop a virus from making copies of itself. Paxlovid is authorized for emergency use but not fully approved by the Food and Drug Administration. Pfizer is working on the necessary paperwork.
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An experimental COVID-19 antiviral appears to be effective at preventing hospitalizations without some of the downsides of other treatments.

A study appearing Wednesday in The New England Journal of Medicine found that a shot of interferon lambda prevented 51% of hospitalizations among people who have been vaccinated — an already low-risk group and one that hasn't been proven to benefit from other treatments.

Interferon lambda still has to go through the regulatory approval process, so it's not available. But the study suggests it could be a viable alternative to authorized treatments like Paxlovid and is superior in some ways.

"The data look quite promising and other treatments have now fallen by the wayside," said Dr. Paul Sax, who directs the division of infectious diseases at Brigham and Women's Hospital in Boston and was not involved in the research.

Monoclonal antibodies, which were effective against earlier variants, are no longer working, leaving people who can't take Paxlovid with fewer options.

"It's been a frustration of mine that it has not been available," Sax said of interferon lambda.

PAXLOVID: The COVID antiviral is keeping people out of the hospital

What is interferon lambda?

Interferons are made by the immune system to limit viral infections and boost the body's ability to fight them.

Lambda is a type of interferon that has effects specifically in the liver and lungs, not the whole body. This limits side effects seen by other interferons, including flu-like symptoms, body aches and depression, said Dr. David Apelian, interim CEO of Eiger BioPharmaceuticals, which makes interferon lambda and provided it for the study.

The company also modifies the interferon through a process called pegylation, he said, to allow for longer-lasting, more effective distribution throughout the body.

"What this drug is doing is trying to augment our body's own response to infection, to try to hasten clearance," Sax said.

For chronic infections like hepatitis D, which Eiger is also testing with interferon lambda, the drug needs to be taken weekly for an extended period of time.

For an acute infection like COVID-19, one shot seems to be enough to boost the body's ability to clear the virus, Apelian said.

The company is also testing it against flu and RSV, hoping that eventually interferon lambda can treat a wide range of respiratory viruses.

Because it targets the immune system, rather than a particular viral variant, interferon lambda should remain useful as the virus that causes COVID-19 continues to evolve and even in the face of new viruses, said Dr. Jeffrey Glenn, the Stanford University virologist who led the new study.

"We can still save millions of lives if we can get this into people," he said.

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What the study showed

More than 900 people who received a shot of interferon lambda in Canada and Brazil were compared with more than 1,000 who received a placebo. Only 2.7% of the mostly vaccinated people in the interferon group had to be hospitalized, compared to 5.6% of those who received a placebo.

The effects were seen as variants of the virus that causes COVID-19 changed in both countries. Patients who received the shot had a lower viral load a week later than those who received placebo.

The people who took lambda interferon suffered no more side effects than those who received a placebo. Investigators "couldn't tell who was on the drug and who was on placebo," Glenn said.

So far, the drug has been used in 3,000 patients in 20 clinical trials, Glenn said.

What are its advantages?

Interferon lambda has several advantages over other treatments used to keep COVID-19 patients from developing severe disease.

Paxlovid, the most effective preventative so far, interferes with a number of commonly used medications, including blood thinners and some cancer drugs.

Doctors often hesitate to prescribe Paxlovid to people who need it most – older people with health issues – because they would have to stop these medications for the five days they take the drug. Interferon lambda does not interfere with other medications.

Paxlovid also requires patients to take 30 pills over five days, while interferon lambda is a single shot, so no one has to remember to complete their doses, Glenn said.

And interferon lambda targets a part of the virus that doesn't change, so it's likely to protect against all variants of SARS-CoV-2. There is some chance that the virus will eventually evolve to evade Paxlovid.

Paxlovid reduced the risk of hospitalization or death by 44% in vaccinated adults over the age of 50, but the other available antiviral, molnupiravir, did not reduce hospitalization or death in vaccinated people at high risk.

The fact that interferon lambda was able to reduce hospitalization among vaccinated people, who are less likely to have a severe outcome, shows the value of the drug, Sax said.

Getting it approved

Data from the newly published study has been available for nearly a year and Sax said he thought the drug would have been approved long ago.

But the Food and Drug Administration determined that the study was not adequate to win authorization and said more data was needed. Eiger not yet managed to fund another COVID-19 trial.

Apelian said he hopes some countries, perhaps China and Australia, will authorize the drug shortly, allowing it to prove its usefulness.

He sees it as particularly relevant in the face of new variants for which vaccines might not be a good match. Infereron lambda could be used to protect people as new vaccines are manufactured, he said.

The company has 100,000 doses already produced and can readily make 10 million more, he said.

"We're well positioned for looking at different opportunities right now," he said.

Contact Karen Weintraub at

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This article originally appeared on USA TODAY: New COVID injection may be promising Paxlovid alternative