UK’s affirmation for AstraZeneca vaccine lead to various 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regimen for the vaccine was an unexpected move by Britain’s medicines regulator based on its own analysis of as-yet-unpublished data and it raised fresh questions about the efficacy of a vaccine which has yet to be approved in other countries.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 vaccine has been plagued with uncertainty about its most effective dosage ever since data published last month showed a half-dose followed by a full dose had a 90% success rate while two full shots were 62% effective.

Oxford researchers said that the more successful outcome was an “intriguing result” that merited further testing.

Instead, Pirmohamed said a higher success rate may be due to a longer gap between the administration of the first and second shots.

“The low dose/standard dose regimen, although it has been quoted to have an efficacy of 90%, this is confounded by the fact that the interval between the first and second dose was quite long,” Pirmohamed told a news conference.