Post-Antiviral Cases Puzzle Doctors

"U.S. health authorities and researchers are investigating why some people who appeared to recover from Covid-19 after taking Pfizer Inc.'s antiviral pill developed symptoms again soon after.

Paxlovid is supposed to treat the newly infected, keeping them out of the hospital. Within two weeks of appearing to get better, however, some users experienced cold-like symptoms such as sore throat and cough, according to physicians and case reports.

The rebound cases haven't resulted in severe disease so far. Doctors and health authorities still encourage Paxlovid's use among people at high risk of developing severe Covid-19.

Yet the cases are the latest puzzle confronting health authorities, researchers and physicians trying to stay ahead of the virus. The health experts said they aren't sure if the relapsed patients are contagious. Nor are they sure what causes the rebounds, theorizing that patients may be taking Paxlovid too early or not long enough. The experts also don't know how common the rebounds are, though Pfizer said its real-world data indicates the relapses occur in fewer than 1 in 3,000 patients.

Meantime, doctors said they were wrestling with how to handle the cases, although some doctors are recommending patients restart isolation.

"This is something public health agencies will have to wrap their heads around and figure out what to do," said Michael Charness, chief of staff at the VA Boston Healthcare System.

Pfizer Chief Executive Albert Bourla said the current label doesn't prohibit a second course of treatment, if doctors determine it is needed.

Recently, however, the Food and Drug Administration said there wasn't evidence of a benefit from giving a longer course of treatment or repeating treatment in rebound patients.

The FDA reiterated Paxlovid's effectiveness and encouraged people at high risk of severe Covid-19 who are newly infected to talk with their doctors about treatment.

The FDA, which didn't mention a risk of relapse in its original prescribing instructions for doctors, hasn't tweaked the directions so far. It declined to say what, if anything, it has told doctors about how to handle the cases.

The FDA is reviewing clinical-trial data. National Institute of Allergy and Infectious Diseases researchers are planning to examine how often the rebound cases occur, why and whether extending treatment is a remedy, a spokeswoman said.

Pfizer said it remains confident in Paxlovid's effectiveness at preventing hospitalization and death in high-risk people, a spokesman said.

The company said a virus developing resistance doesn't appear to be the cause. Pfizer is reviewing data from its clinical trials and monitoring real-world use of the drug.

People with new infections at high risk of developing severe disease can take the pills over five days at home to avoid going to the hospital.

The drug, which was found to be 88% effective in its pivotal trial, works by blocking activity of a key enzyme known as protease that the virus needs to replicate.

Since their authorization in late December, the pills have become a go-to Covid-19 treatment. Some 80,000 people in the U.S. have taken Paxlovid, according to Pfizer.

Neither the FDA nor CDC said it had a tally of the number of cases." [1]

1. U.S. News: Post-Antiviral Cases Puzzle Doctors
Hopkins, Jared S. 
Wall Street Journal, Eastern edition; New York, N.Y. [New York, N.Y]. 11 May 2022: A.3.