The Factors That Promote Vaccine Hesitancy, Rejection, or Delay in Parents.

Vaccines are some of the most cost-effective public health interventions for reducing disease burden and mortality. However, in recent years, health systems have faced a growing challenge with increasing number of parents who choose not to vaccinate their children. This decision has important implications for the health of communities worldwide, and despite a considerable amount of research that reinforces vaccine effectiveness and safety, there is uncertainty surrounding the factors that may encourage vaccine hesitancy in parents. In this interpretive review of 34 qualitative studies, we examine the factors that bolster vaccine hesitancy, rejection, and delay, and identify the overlaps and relationships between these factors. We depict our findings using the metaphor of a gear train where each gear represents one of seven factors: previous experiences; "natural" and "organic" living; perceptions of other parents; experiences interacting with health care providers; information sources, challenges, and preferences; distrust in health system players; and mandatory vaccine policies.