Vaccination is used worldwide to prevent infectious diseases. However, vaccination programmes in western countries face challenges in sustaining high coverage rates. The aim of this study was to explore how parents in Denmark make a decision about whether to allow their child to receive a Bacille Calmette Guerin vaccine at birth for the purpose of achieving non-specific effects on the immune system. | “Lay epidemiology”: An important factor in Danish parents’ decision of whether to allow their child to receive a BCG vaccination: A qualitative exploration of parental perspective