Opinion: Pfizer, AstraZeneca … or both? A mixed approach may hold promise.

At the start of the COVID-19 pandemic, it was unclear whether researchers would be able to create a single working vaccine, which makes it all the more surprising that the latest immunization dilemma arises from having multiple vaccine options. Because of unpredictable supply and some concerns about an exceedingly rare but serious clotting risk from the AstraZeneca vaccine, public health officials in some parts of the world that have relied heavily on that shot have recently issued new guidance on mixing and matching different COVID-19 vaccines.