June 7 (Reuters) - A 15-day course of Pfizer's ( PFE )

COVID-19 antiviral treatment Paxlovid did not relieve symptoms

of long COVID, according a study by Stanford University

researchers.

Currently, there are no proven treatments specifically for

long COVID in which a host of symptoms can last for many months

after initial coronavirus infection.

Scientists and patients had hoped that Pfizer's ( PFE ) two-drug

oral treatment would ease symptoms of long COVID after anecdotal

reports of patients who said Paxlovid helped them.

But the 15-week, 155-participant study failed to show that a

15-day course helped more than a placebo in reducing fatigue,

brain fog, shortness of breath, body aches, or gastrointestinal

or cardiovascular symptoms. Trial participants, on average, had

been sick more than 16 months before enrolling in the trial.

"We did not see a measurable difference based on patient

reported outcomes in the six composite symptoms together,"

Stanford Medicine Professor Dr. Upinder Singh said in an

interview. "We didn't see a benefit in individual symptoms

either."

Dr. Singh said she believes that further study of the

treatment for long COVID still has merit, perhaps in longer

courses than 15 days or in patients who haven't been sick for as

long.

The study did show that Paxlovid, which is currently

prescribed as a 5-day course early after infection or symptom

onset, is safe when used for 15 days, she added.

Pfizer ( PFE ) said in a statement that the results will not impact

its other planned collaborative studies of Paxlovid as a

potential treatment for long COVID.

Paxlovid is the most commonly prescribed at home treatment

for COVID-19 in the U.S. It is approved to treat COVID in adults

who are at risk of severe complications from the illness.

In Pfizer's ( PFE ) original clinical trial, Paxlovid was shown to

reduce hospitalizations and death from COVID by around 90% for

unvaccinated people at risk for serious disease. In another

trial, Pfizer ( PFE ) was not able to show benefit for those considered

at standard risk, including vaccinated patients.

Pfizer ( PFE ) funded the long COVID trial. Aside from Stanford

researchers, scientists from Kaiser Permanente North California

and Pfizer ( PFE ) also contributed to the study.