In accordance with its mandate to provide guidance to Member States on health policy matters, WHO issues a series of regularly updated position papers on vaccines and combinations of vaccines against diseases that have an international public health impact, and on vaccination-related policy questions particularly concerning the use of vaccines in large-scale immunization programmes. They summarize essential background information and conclude with the current WHO position. This position paper addresses a cross-cutting issue which is relevant for all injectable vaccines and reflects the recommendations of WHO's Strategic Advisory Group of Experts (SAGE) on immunization. These recommendations were discussed by SAGE at its April 2015 meeting. The evidence presented at the meetings can be accessed at http://www.who.int/immunization/sage/previous/en/index.html.