Four decades ago in 1974, the World Health Organization (WHO) launched the Expanded Programme on Immunization (EPI). The EPI blueprint laid out the technical and managerial functions necessary to routinely vaccinate children with a limited number of vaccines, providing protection against diphtheria, tetanus, whooping cough, measles, polio, and tuberculosis, and to prevent maternal and neonatal tetanus by vaccinating women of childbearing age with tetanus toxoid. The purpose of EPI was simple and straightforward—to deliver multiple vaccines to all children through a simple schedule of child health visits.1 At the time, basic health systems in most lower- and lower-middle income countries (LLMICs) were weak to nonexistent. Vaccine coverage levels among children younger than 1 year of age were less than 5%.2 By 1990, most LLMICs had institutionalized immunization programs based on the EPI blueprint. In 1991, the global target of vaccinating 80% of the world's children was declared to have been met, saving millions of lives. The capacities and capabilities of countries built through the EPI blueprint were responsible for such significant gains.2

Since then, more vaccines have been added to national immunization schedules, and the contribution of immunization programs to ongoing declines in infant and child mortality has increased commensurately.3,4 As of 2014, WHO has recommended that all immunization programs add vaccines against hepatitis B, Haemophilus influenzae type b, Streptococcus pneumoniae, rotavirus, rubella, and human papillomavirus (in girls). However, the full benefits of these vaccines has yet to be realized. WHO estimates 29% of deaths among children 1–59 months of age are vaccine-preventable.5 This gap is due largely to systems weaknesses in immunization programs that can be improved. With the addition of new vaccines, the complexity and costs of routine immunization increase.2,3,6,7 More vaccinations to protect against more diseases requires additional and better communication between health workers and caregivers as well as greater cold chain capacity. New vaccines and doses that expand immunization beyond infancy extend the benefits of vaccines across the life spectrum into adolescence and adulthood. Moreover, health systems in general are becoming more complex as new programs and services are added.