What to know about "rebound" in COVID symptoms after taking Paxlovid

Scientists and federal agencies say they are investigating reports of Americans who say they faced a resurgence of COVID-19 soon after finishing off a course of Paxlovid, Pfizer's antiviral treatment for the disease. 

Often referred to as a "rebound" or "relapse" of COVID-19 after taking the standard five days of Paxlovid pills, experts say key questions need to be answered around why it happens, who is being affected, and how doctors should handle the cases. 

For example, one report from Veterans Affairs doctors describes a 71-year-old man who saw his COVID-19 symptoms quickly clear up after two days of taking the drug. But four days after finishing the full course of Paxlovid, his symptoms — including a runny nose and sore throat — returned for a few more days.