Callaghan's primary research interests are in health policy, health politics, and the study of public health attitudes. He has published extensively on the social, psychological, and political underpinnings of vaccine hesitancy in the US. He is also currently serving as a commissioner on the Lancet Commission to understand Vaccine Refusal, Acceptance, and Demand in the United States.
Quote: “Considerable work is needed to increase vaccine uptake among the hesitant. In these efforts at convincing the hesitant, it is important to recognize that trusted communicators should be leading the way but that a ‘one size fits all’ approach will not work and that different messages will be needed to reduce hesitancy among different groups.”