Researchers at Washington University School of Medicine in St. Louis, led by Michael S. Diamond, MD, PhD, the Herbert S. Gasser Professor of Medicine, immediately started investigating the new variant of SARS-CoV-2, the virus that causes COVID-19. Within a few weeks, they had data showing that omicron was a mixed bag: It could resist most antibody-based therapeutics, but it was less able to cause severe lung disease, at least in mice and hamsters.