Press Release - WHO with support of the Strategic Advisory Group of Experts (SAGE) on Immunization and its COVID-19 Vaccines Working Group is reviewing the emerging evidence on the use of heterologous priming schedules (also known as mix and match schedules). In a heterologous priming schedule, the second dose uses a different vaccine product than the first dose. By contrast, heterologous boosting refers to the administration of a vaccine from a different vaccine platform from the vaccine that was used to complete the pri
