A Model for a Just COVID-19 Vaccination Program: Scientists have now produced apparently effective vaccines at sufficient scale to vaccinate most vulnerable populations in the United States in the next few months, and the U.S. population more broadly in the next year. How can the distribution protect the masses without perpetuating inequalities? There are no simple answers but the way forward must be informed by understanding the complex interactions among the virus, vaccines, individual health and socio-economic status, and the societal structures in which these are all embedded.