WHO immunization policy recommendations are published in vaccine position papers on the basis of recommendations made by the Strategic Advisory Group of Experts on Immunization (SAGE). WHO vaccine position papers are updated three to four times per year. Vaccines listed on the 2019 Model List are those for which there is a recommendation from SAGE and a corresponding WHO position paper as at December 2018. The February 2007 version of the WHO position paper for mumps vaccine is attached. The most recent versions of the WHO position papers, reflecting the current evidence related to a specific vaccine and the related recommendations, can be accessed at any time on the WHO website at: http://www.who.int/immunization/documents/positionpapers/en/index.html. Vaccine recommendations may be universal or conditional (e.g., in certain regions, in some high-risk populations or as part of immunization programmes with certain characteristics). Details are available in the relevant position papers, and in the Summary Tables of WHO Routine Immunization Recommendations available on the WHO website at: http://www.who.int/immunization/policy/immunization_tables/en/index.html. Selection of vaccines from the Model List will need to be determined by each country after consideration of international recommendations, epidemiology and national priorities.