Labor Economics Conference, the IZA Junior/Senior Symposium, the IZA World Labor Conference, the ASHEcon Annual Conference, the IHEA World Congress, the WEAI Annual Conference, and various universities, as well as insightful comments three anonymous referees, Desislava Byanova, David Chan, Olivier Deschenes, Mark Duggan, Melanie Guldi, Bree Lang, Michelle Marcus, Sarah Reber, Peter Kuhn, Maya Rossin-Slater, Heather Royer, and Hannes Schwandt. White has received no financial support for this study and has no relevant material financial interests that relate to the research described in this paper. Certain calculations use data from the National Center for Health Statistics multiple cause of death files (1994-2016), as compiled from data provided by the 57 vital statistics jurisdictions through the Vital Statistics Cooperative Program. Some of the data (that is, NCHS Vital Statistics Mortality data and California OSHPD hospital data) are not publicly available. Interested researchers can apply for access to these data Vaccination represents a canonical example of externalities in economics, yet there are few estimates of their magnitudes. I estimate social and externality benefits of influenza vaccination in two settings. First, using a natural experiment, I estimate the impacts of aggregate vaccination rates on mortality and work absences in the United States. Second, I examine a setting with large potential externality benefits: vaccination mandates for healthcare workers. I find that the social benefits of vaccination are substantial, most of benefits operate through an externality, and the benefits of healthcare worker vaccination are particularly large.