Vaccination: The World Health Organization, with the support of the Strategic Advisory Group of Experts (SAGE) on Immunization and its COVID-19 Vaccines Working Group, continues to review the emerging evidence on the need for and timing of a booster dose for the currently available COVID-19 vaccines which have received Emergency Use Listing (EUL). This statement reflects the current understanding of vaccine performance and supply as presented to SAGE on 7 December 2021. It summarizes and contextualizes current evidence on booster vaccination.