Achieving high vaccination coverage of priority groups should be the focus of national immunization programmes, using either the same vaccine for the different doses (homologous schedule) or different vaccines (heterologous schedules).
Interchangeability of vaccine platforms for adults allows for flexibility, for example in the face of constrained or unpredictable supply. However, until sufficient evidence is available on interchangeability of paediatric formulations of COVID-19 vaccines, it remains standard practice to use the same product to complete primary schedule for children (<12 y.o.).
Variant-containing vaccines have been approved for use as booster doses. Until supportive evidence or regulatory approval becomes available, they should not be used as the primary series.