COVID-19 vaccines may be the key to ending the pandemic. Kate Langwig, an infectious disease ecologist and epidemiologist, discusses the mechanisms behind vaccine efficacy and the roadblock to herd immunity. Patrick Butler, a senior research associate at the Sanghani Center, and Nikhil  Muralidhar, a Ph.D. student in computer science, dive into the work of using open-source indicators to model and forecast flu and COVID-19.