A study by researchers at Mass General Brigham hospital in Boston found that one in five COVID-infected individuals treated with antiviral medication Paxlovid experienced viral rebound, shedding live and potentially contagious virus after an initial negative test. The rebound phenomenon was more common than expected, occurring over 20% of the time with Paxlovid. The study highlights the need for patient counseling and re-testing during Paxlovid treatment, despite its effectiveness in reducing hospitalization and death in severe COVID-19 cases.