Since the last century, vaccination has been one of the most important tools we possess for the prevention and elimination of disease. Yet the tremendous gains from vaccination are now threatened by a growing hesitance to vaccinate based on a variety of concerns or objections. Geographic clustering of some families who choose not to vaccinate has led to a number of well-publicized outbreaks of vaccine-preventable diseases. Of note is that some of these outbreaks are centered within some Christian religious groups that increasingly avoid vaccination due to moral concerns, fears about safety, or doubts about the necessity of vaccines. We argue from the perspective of Catholic social teaching on why there is a moral duty to vaccinate.