An analysis of real-world data from more than 1.2 million patients from health systems in four geographically dispersed states -- Indiana, Oregon, Texas and Utah -- conducted by the U.S. Centers for Disease Control and Prevention’s VISION Network, has determined both the number of adults needed to be vaccinated to prevent one COVID-19 associated hospitalization and the number needed to be vaccinated to prevent one COVID-19 associated emergency department (ED) visit. This study is one of the first, largest and most comprehensive studies to present clear measurement, by age groups, of how widespread vaccination needs to be to provide protection against serious and moderate disease in adults.