Evidence mounts for need to study Pfizer oral antiviral treatment Paxlovid for long COVID: Researchers

In two of the cases, the patients "were able to access Paxlovid antiviral therapy and feel that their long COVID symptoms improved substantially," said Dr. Michael Peluso, whose was published online on Research Square.

In the third, a patient was given the drug as prescribed to treat an acute infection. While his symptoms improved at first, they rebounded shortly after he stopped taking the drug, and the man later developed long COVID.

"There's been a lot of hope that early antiviral therapy, in addition to preventing severe COVID, will prevent long COVID. And that might be true, but this case suggests that it won't be true 100% of the time," Peluso said.

All three patients, who were in their 40s and had previously been vaccinated against COVID-19, were enrolled in the UCSF long COVID trial known as LIINC.

The cases are not definitive, but they offer clues about long COVID, a poorly understood condition that has left researchers scrambling to find its possible causes.

"It provides evidence that we really need to study this soon, and ... systematically, which means randomized trials," said Peluso.

He said the UCSF team would love to conduct such a study, but it would require funding from agencies such as the National Institutes of Health, and the drugmaker.

Pfizer spokesman Kit Longley said company does not have any current long COVID studies underway, but was monitoring data from ongoing clinical studies and real-world evidence, and may explore the issue further.

"Collectively, there is now ample rationale to design and implement prospective controlled studies of antiviral therapies, including Paxlovid," said Dr. Steven Deeks of UCSF and a senior author on the study.

Read also: Paxlovid not be included in national treatment guidelines for COVID-19, says ICMR