Ensitrelvir, the COVID-19 antiviral made by the pharmaceutical company Shionogi. Credit - Courtesy Shionogi
When a young, healthy person in the U.S. catches COVID-19, there’s not much they can do except stay home and rest. The antiviral drug Paxlovid is widely available, but it’s only approved for people at high risk of severe disease, such as older adults and people with underlying conditions. The U.S. Food and Drug Administration (FDA) hasn’t approved any drugs that can treat COVID-19 among people who are unlikely to get very sick or die, but nonetheless would like some relief from their symptoms.
These drugs do exist, though. Antivirals currently available overseas seem to be effective at shortening the length and treating the symptoms of mild-to-moderate cases of COVID-19—but it’s anyone’s guess if and when they’ll make the jump to the U.S. market.
A study published in the New England Journal of Medicine in January showed promising results associated with the drug simnotrelvir, which is made by Simcere Pharmaceutical and is currently available in China under the brand name Xiannuoxin. People who took simnotrelvir within three days of developing COVID-19 recovered faster than people who took a placebo, the researchers found. Most of the roughly 1,100 people in the study were young and fully vaccinated and half did not have any specific risk factors for serious disease, which suggests simnotrelvir could work well across much of the general population.
It’s unclear whether Simcere is seeking FDA approval; representatives from the company did not respond to TIME’s requests for comment about if and when it may apply.
At the moment, the drug with perhaps the best shot at cracking the U.S. market seems to be the antiviral ensitrelvir, which is made by the pharmaceutical company Shionogi & Co., Ltd., and has been approved in Japan under the brand name Xocova since 2022. In April 2023, the drug received “Fast Track” designation from the FDA, a status meant to expedite the agency’s review process.
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When taken shortly after getting sick, ensitrelvir shortens the length of time it takes for people with mild-to-moderate COVID-19 to test negative and recover from certain symptoms, research shows. Some preliminary data also suggest people who take ensitrelvir may be less likely to have Long COVID symptoms later on.
The drug could be a big deal both for patients and public health, says Simon Portsmouth, head of clinical development at Shionogi Inc., Shionogi's U.S. subsidiary. The company’s research shows that people who take ensitrelvir stop shedding infectious virus sooner than people who don’t, which means “the potential for reducing infectiousness and onward transmission in the community is another benefit,” Portsmouth says.
Dr. Eric Topol, director of the Scripps Research Translational Institute, says having multiple antivirals to choose from in the U.S. would also be a good insurance policy, since it’s feasible that the virus could someday mutate to become resistant to Paxlovid.
Ensitrelvir also seems to have fewer side effects than Paxlovid, which is known for its bad aftertaste and long list of drug interactions, says Stefan Sarafianos, a professor at Emory University who researches antivirals. It may also come with lower chances of “rebound” positive tests, he adds. Solving some of those problems would be an upgrade for U.S. public health, Sarafianos says, since they partially explain why Paxlovid is underused even among people at high risk of severe disease.
Portsmouth declined to comment on ensitrelvir’s regulatory timeline, saying only that Shionogi needs to complete additional clinical trials before anything else can happen. (Last year, the CEO of Shiongi & Co., Ltd., estimated the drug could be approved in the U.S. at some point in 2024.) The company has also signed a licensing agreement that will allow ensitrelvir to be manufactured and distributed in 117 countries, pending appropriate regulatory approvals, to boost access in low- and middle-income nations.
In a statement provided to TIME, an FDA spokesperson said the agency “remains committed to providing product-specific advice to drug developers to facilitate the development of new drug products to treat or prevent COVID-19.” But it did not comment on the likelihood or timing of simnotrelvir, ensitrelvir, or other COVID-19 antivirals receiving approval.
It would be good for Americans to have antiviral choices, Topol says, but the regulatory process for new drugs can be long and winding. “If [other antivirals] do come here,” he says, “it’s probably not going to be imminent.”
Write to Jamie Ducharme at email@example.com.