As the Americas undergo profound demographic change and there are more persons aged 65 years or older than children younger than 5 years, it is crucial to recognize that national immunization programs must be redesigned to ensure comprehensive protection for individuals across the lifespan. By adopt...ing a life course approach (LCA) to immunization, vaccination programs can be tailored to close immunity gaps at different stages of life. The life course approach foresees the establishment of multiple strategies to reduce missed opportunities for vaccination according to age group. This technical document explains the key concepts of the LCA with a focus on immunization by vaccination, as well as the underlying biological mechanisms that require the application different vaccines at different life stages according to changes to the immune system and in the epidemiological situation of a community. more