During the first COVID-19 wave, when Saumitra Das and colleagues were sequencing thousands of samples every day to check for SARS-CoV-2 variants as part of INSACOG, the Government of India's genome surveillance initiative, they were racing against time to track mutations as they appeared. "If we wanted to predict whether one of these mutations was going to be dangerous from a public health perspective, we needed an assay system," says Das, Professor at the Department of Microbiology and Cell Biology (MCB), Indian Institute of Science (IISc).