Massachusetts’ first known case of SARS-CoV-2 arrived on January 29. The patient was a university student who had been traveling in Wuhan, China, and was quickly quarantined at home. Despite early vigilance, the disease had started to spread widely in the state by early March. In collaboration with the Broad Institute and the Massachusetts Department of Public Health, Jacob Lemieux, an infectious disease fellow at Massachusetts General Hospital, led a team of dozens of researchers trying to pin down the precise origin and spread of the virus. They performed whole genome sequencing of 772 virus samples from the Boston area, including nearly all cases confirmed during the first week of the epidemic. The data revealed more than 80 introductions into the Boston area, including events that spread the disease far and wide.

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