Kelsey Moran and Gail Rosenbaum are co-primary authors on this work. This research was supported by the NBER Roybal Center for Behavior Change in Health (NIA P30 AG034532). We thank Dr. John Pellegrino who suggested the lottery incentive idea. We also thank Katy Milkman, Richard Thaler, and seminar participants at MIT Sloan, Harvard Kennedy School, and Harvard Health Care Policy for helpful comments. We thank Carroll Walter for project management support, Dr. Stanley Martin for his support of vaccine outreach at Geisinger, the Geisinger Business Intelligence and Advanced Analytics team for assistance extracting data, and the Geisinger Marketing team for help implementing the messages. The views expressed herein are those of the authors and do not necessarily reflect the views of the National Bureau of Economic Research.