Health Canada is reviewing evidence for mixing COVID-19 vaccines as questions linger around the AstraZeneca vaccine, already administered to hundreds of thousands of Canadians who are due for a second dose. A rare blood clotting complication has been identified in a small number of recipients and there is uncertainty around Canada’s future supply of AstraZeneca. A study in the UK is looking at the safety and efficacy of mixing vaccines, and its conclusions could help to inform Canada’s direction. Some researchers are hopeful that mixing vaccines could prove to be not only safe, but more effective than receiving two of the same kind.