In 2016 and 2017, a surge of mumps cases at Boston-area universities prompted researchers to study mumps virus transmission using genomic data, in collaboration with the Massachusetts Department of Public Health and local university health services. As the outbreaks unfolded, the teams analyzed mumps virus genomes collected from patients, revealing new links between cases that first appeared unrelated and other details about how the disease was spreading that weren’t apparent from the epidemiological investigation.