The Pfizer drug Paxlovid. A new study said the drug failed...

The Pfizer drug Paxlovid. A new study said the drug failed to treat symptoms of long COVID.  Credit: AP/Stephanie Nano

A leading antiviral pill used to prevent severe disease from the coronavirus failed to treat symptoms from the often debilitating syndrome known as long COVID, according to a new study released Friday by researchers from Stanford University.

The randomized, double-blinded clinical trial was the first to study the effect of Paxlovid on long COVID. The FDA-approved oral medication has proven successful in treating adult patients at severe risk from COVID, if taken within five days of experiencing symptoms, but the trial looked at whether it could treat patients who have continued to experience health problems months and years after their initial infection.

While researchers found a 15-day course of Paxlovid proved safe as an extended-duration treatment — it's typically prescribed for only five days — the drug failed to lessen the symptoms associated with long COVID, including brain fog, fatigue and respiratory issues.

The findings were published Friday in JAMA Internal Medicine.

“While there are now improved therapies and treatment practices for acute COVID, there’s nothing FDA-approved for long COVID,” said Dr. Linda Geng, a clinical associate professor of primary care and population health at Stanford Medicine, and one of the trial's two lead investigators. “People continue to suffer and the numbers keep piling up,”

Despite the outcome of the trial, there remains some anecdotal evidence of Paxlovid providing relief for long-COVID symptoms, said Geng, who codirects Stanford’s long-COVID clinic.

An estimated 17.6% of adults, or more than 45 million Americans, have experienced, at one point, symptoms of long COVID, according to a recent federal Household Pulse Survey.

There is no known cure for long COVID — only medication and therapies to treat some of the symptoms that long COVID causes, experts said.

Dr. Astha Muttreja, a physician at the Stony Brook Medicine's post-COVID Clinic in Lake Grove, said there had been “cautious optimism” that Paxlovid would be a potential treatment method for long COVID.

“But what I think it really demonstrates is that we have to look further to some of the other potential causes of long COVID,” Muttreja, said. “There's still a lot we don't know understand about this condition.”

The clinical trial, conducted between November 2022 and September 2023, followed 155 residents of the San Francisco Bay Area who tested positive for the virus an average of 16 months prior and were continuing to experience several of the most common systems of long COVID. The participants were an average of 43-years-old and all but two had been vaccinated.

Half of the study participants were given a 15-day course of Paxlovid. The others received a placebo, along with low dosages of one of two other drugs that, combined, constitute Paxlovid.

Researchers found no statistically significant difference between the two groups, nor a measurable reduction in the severity of the six core long COVID symptoms — fatigue, brain fog, shortness of breath, body aches, and cardiovascular or gastrointestinal symptoms — or in secondary outcomes such as seated and standing blood pressure and heart rates.

Dr. Ziyad Al-Aly, a clinical epidemiologist and chief of research and development at the VA St. Louis Health Care System, said while the results were “disappointing” they still leave the door open for future studies, particularly among patients treated with Paxlovid quicker for their long COVID symptoms.

“Although this did not work, it doesn't mean the door is closed on Paxlovid's effectiveness,” said Al-Aly, who has studied the effects of long COVID for years and is preparing to release new research on how the illness has changed as the virus has continued to evolve. “Perhaps a higher dose; a longer duration; a combination of therapy or earlier treatment might work. It would have been better news if it was a positive trial. But I am still hopeful.”

A leading antiviral pill used to prevent severe disease from the coronavirus failed to treat symptoms from the often debilitating syndrome known as long COVID, according to a new study released Friday by researchers from Stanford University.

The randomized, double-blinded clinical trial was the first to study the effect of Paxlovid on long COVID. The FDA-approved oral medication has proven successful in treating adult patients at severe risk from COVID, if taken within five days of experiencing symptoms, but the trial looked at whether it could treat patients who have continued to experience health problems months and years after their initial infection.

While researchers found a 15-day course of Paxlovid proved safe as an extended-duration treatment — it's typically prescribed for only five days — the drug failed to lessen the symptoms associated with long COVID, including brain fog, fatigue and respiratory issues.

The findings were published Friday in JAMA Internal Medicine.

“While there are now improved therapies and treatment practices for acute COVID, there’s nothing FDA-approved for long COVID,” said Dr. Linda Geng, a clinical associate professor of primary care and population health at Stanford Medicine, and one of the trial's two lead investigators. “People continue to suffer and the numbers keep piling up,”

Despite the outcome of the trial, there remains some anecdotal evidence of Paxlovid providing relief for long-COVID symptoms, said Geng, who codirects Stanford’s long-COVID clinic.

An estimated 17.6% of adults, or more than 45 million Americans, have experienced, at one point, symptoms of long COVID, according to a recent federal Household Pulse Survey.

There is no known cure for long COVID — only medication and therapies to treat some of the symptoms that long COVID causes, experts said.

Dr. Astha Muttreja, a physician at the Stony Brook Medicine's post-COVID Clinic in Lake Grove, said there had been “cautious optimism” that Paxlovid would be a potential treatment method for long COVID.

“But what I think it really demonstrates is that we have to look further to some of the other potential causes of long COVID,” Muttreja, said. “There's still a lot we don't know understand about this condition.”

The clinical trial, conducted between November 2022 and September 2023, followed 155 residents of the San Francisco Bay Area who tested positive for the virus an average of 16 months prior and were continuing to experience several of the most common systems of long COVID. The participants were an average of 43-years-old and all but two had been vaccinated.

Half of the study participants were given a 15-day course of Paxlovid. The others received a placebo, along with low dosages of one of two other drugs that, combined, constitute Paxlovid.

Researchers found no statistically significant difference between the two groups, nor a measurable reduction in the severity of the six core long COVID symptoms — fatigue, brain fog, shortness of breath, body aches, and cardiovascular or gastrointestinal symptoms — or in secondary outcomes such as seated and standing blood pressure and heart rates.

Dr. Ziyad Al-Aly, a clinical epidemiologist and chief of research and development at the VA St. Louis Health Care System, said while the results were “disappointing” they still leave the door open for future studies, particularly among patients treated with Paxlovid quicker for their long COVID symptoms.

“Although this did not work, it doesn't mean the door is closed on Paxlovid's effectiveness,” said Al-Aly, who has studied the effects of long COVID for years and is preparing to release new research on how the illness has changed as the virus has continued to evolve. “Perhaps a higher dose; a longer duration; a combination of therapy or earlier treatment might work. It would have been better news if it was a positive trial. But I am still hopeful.”

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