The first oral antiviral for treating COVID-19, Merck & Co.’s molnupiravir, received approval from the U.K. Medicines and Healthcare products Regulatory Agency on 4 November. But the approval, for people at high risk of severe disease, comes as a prominent virologist has suggested using molnupiravir could do far more harm than good, potentially unleashing new, deadlier variants of SARS-CoV-2. Other virologists say the concern is worth tracking but is largely hypothetical, for now.