Pfizer’s antiviral COVID-19 treatment Paxlovid is safe and effective at treating adults with mild to moderate COVID-19 who are at high risk of progressing to severe disease, including hospitalization or death, according to a Food and Drug Administration (FDA) staff report.

In addition, the report said the drug doesn’t cause patients to “rebound” after taking it.

The report was released in briefing documents ahead of an agency advisory committee meeting on Thursday, where outside advisers will discuss whether to recommend Paxlovid for full approval.

Paxlovid is currently on the market through an emergency use authorization granted in 2021. The FDA typically follows the advice of its outside panels but is not required to.

Pfizer and other companies are anticipating a significant drop in revenue in 2023 compared to 2022 as the U.S. government ends its purchase agreement for COVID-19 vaccines and treatments. 

The company expects $8 billion in Paxlovid revenue this year, down 58 percent from 2022.

More than 11 million patients worldwide have received Paxlovid for the treatment of COVID-19 since it was first authorized for emergency use in December 2021, including more than 8 million in the United States. 

The report found Paxlovid is not associated with cases of “rebound,” in which patients test positive or have symptoms days after a 5-day course of the drug is completed. 

FDA found the overall symptom rebound rates in Pfizer’s clinical trial ranged from 10 percent of patients to 16 percent, with no evidence of a higher rate of symptom rebound or moderate symptom rebound in Paxlovid recipients relative to placebo.

That was also the case regardless of patients’ risk of severe disease, or whether the omicron variant or the earlier delta variant was dominant, the staff report found.

Questions about Paxlovid rebound have swirled since the drug was first authorized, and anecdotal reports led to speculation. Last year, both President Biden and his former chief medical adviser Anthony Fauci experienced rebound cases after taking Paxlovid.  

Despite the widespread reports, FDA said “it has been challenging to determine the direct contribution of Paxlovid treatment to virologic or symptomatic rebound from published reports.”

The meeting is also likely to examine whether Paxlovid is just as effective against omicron as it was for earlier variants. 

While clinical trial data were limited, FDA said it’s reasonable to conclude, based on the available virology data, “that Paxlovid is likely to retain clinical efficacy” in adults with COVID-19 caused by the omicron variant who are at high risk of progression to severe disease.

Paxlovid has been most effective in high-risk people who are not vaccinated and without any prior immunity. But in the current stage of the pandemic, more than 90 percent of U.S. adults have either received a COVID-19 vaccine or had some immunity from a prior infection.

Still, FDA said there’s an important population-level benefit to high-risk people who are vaccinated or previously infected.

There were approximately 4,000 COVID-19-related deaths and 35,000 COVID-19-related hospitalizations each week in the United States in January 2023, FDA noted. Even with a conservative estimate of 25 percent of eligible patients unable to take Paxlovid due to possible side effects, Paxlovid could still lead to 1,500 lives saved and 13,000 hospitalizations averted each week.