No half measures and mind the gap - UK nod for AstraZeneca vaccine raises more questions

British health officials greenlighted the AstraZeneca and Oxford COVID-19 shot on Wednesday but also rebuffed one of their central claims: that a half-dose followed by a standard dose offered more protection against infection.

The reassessment of the best dosing regimen for the vaccine was an unexpected move by Britain’s medicines regulator based on its own analysis of as-yet-unpublished data and it raised fresh questions about the efficacy of a vaccine which has yet to be approved in other countries.

Though cheaper and easier to distribute than rival shots, the Oxford/AstraZeneca...