A small number of COVID-19 patients are relapsing after taking Pfizer's antiviral pill, raising questions about the drug at the center of the U.S. response effort.
Paxlovid has become the go-to option against COVID-19 because of its at-home convenience and impressive results in heading off severe disease.
The U.S. government has spent more than $10 billion to purchase enough pills for 20 million people. But doctors have begun reporting cases of patients who see their symptoms return several days after treatment.
It's one of several questions about how the drug is holding up against a changing virus.
Pfizer mainly studied the drug in unvaccinated patients during the delta wave. But most Americans now have had at least one shot as omicron variants dominate the outbreak.
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