The Oxford vaccine, developed in tandem with AstraZeneca, has so far been covered in the press as a “game-changing” contribution to the coronavirus crisis: cheaper than the mRNA vaccines developed by Moderna and BNT-Pfizer and just as effective and easier to distribute (the vaccine can be stored at fridge temperature).

However, serious questions are now being raised about the way trials for the vaccine have been structured. Hilda Bastian, reporting in the technology magazine, WIRED, unravels the details.

“Monday’s announcement did not present results from a single, large-scale, Phase 3 clinical trial,” she writes. “Oxford AstraZeneca’s data came out of two separate studies: one in the UK that began in May and another in Brazil, which got started at the end of June.”

The drugs were delivered under different dosing regimes and the trial participants had a different profile: no one over the age of 55 took the jab in Brazil. Even the placebo was different. In the UK, volunteers had a meningococcal vaccine; in Brazil, they received a saline injection.

In one of the cohorts, a half dose was administered for the first jab, which came about my accident. It was shown to have 90% efficacy. It has since emerged that no one over the age of 55 was included in the half dose group. The group in which the vaccine showed 62% efficacy included people of all ages. “This demographic difference could be more important than the change to the size of the first dose,” Bastian writes. By contrast, in BNT-Pfizer’s larger phase trial, 41% of volunteers were over 55.

The implication is rather troubling. Bastian notes: “Now it’s over to the drug regulatory agencies around the world. They have to make a decision about this vaccine that was once ahead of the pack, but for which there are still no reliable and rigorous results from a single large phase 3 trial.”