Is the timing of recommended childhood vaccines evidence based

Vaccines undergo extensive testing and review before licensing to evaluate their immunogenicity, safety, and effectiveness in preventing disease.1 For example, prelicensing trials of pneumococcal conjugate and rotavirus vaccines are among the largest randomised controlled trials ever conducted, enrolling tens of thousands of infants.2 3 4 In addition to randomised controlled trials, which produce the highest level of evidence and provide the basis for vaccine licensure, vaccine policy also benefits from the additional supportive evidence obtained from thousands of other types of vaccine studies. Such studies generate critical data regarding age specific immunogenicity, dose and dosing intervals, interaction with other vaccines, duration of immunity, and overall vaccine safety to inform schedules.### What evidence is needed to make the most appropriate schedule?Data from clinical trials represent only a portion of the evidence considered in determining vaccination schedules.5 Burden of disease, immunogenicity, and efficacy studies enable countries to select vaccines and schedules appropriate for their populations, as shown by the recent infographic in The BMJ .6 Vaccine schedules are further refined by considerations such as timing and efficiency of access to the target population to optimise uptake. For childhood vaccines, integration with existing local or national well child visit schedules is a critical consideration. This concept was summarised well in the US Institute of Medicine (IoM) report on the childhood immunisation schedule: “Each new vaccine is approved on the basis of a detailed evaluation of both the vaccine itself and the immunization schedule.” The IoM further stated that randomised controlled trials in which children “would receive less than the full immunization schedule or no vaccines would not be ethical because they would be exposed to a greater risk for the development of diseases and community immunity would be compromised.”5Once vaccines are in general use local surveillance is generally conducted to evaluate their effect on disease burden. …