The pandemic is at its worst, globally, and expert eyes are trained on the role of new variants. Catastrophic surges are tearing across places where some thought the darkest days were already over. In India, where hospitals are running out of oxygen and COVID-19 cases are increasing exponentially, officials are concerned about a “double mutant” version of SARS-CoV-2 called B.1.167. In Brazil, where more than 2,500 people are dying every day, the government is urging people not to get pregnant for fear of variants like P.1. And such variants are giving rise to further variants, as mutations layer on mutations.