The puzzling phenomenon of Paxlovid

Many COVID-19 patients who took the antiviral treatment Paxlovid said their symptoms appear to rebound after taking the five-day course of medication, my colleague Kay Lazar reported. Others went so far to say that after feeling better and testing negative, they then tested positive again a few days later. 

The issue has captured the attention of at least two teams of Boston-area scientists, who are trying to understand what might be fueling the problem.