Oxford Vaccine Shot That Works Better In Smaller Doses Raises Questions

The news reached Sarah Gilbert Saturday evening that the Covid-19 vaccine she’s developed with AstraZeneca Plc appeared to work. But the University of Oxford professor had expected a key number: Was it more than 90% effective, as others have been — or less?

Instead, when her colleague Andrew Pollard called with the results, he wanted to show her slides instead of simple figures. “I didn’t really understand why we would have to go through slides,” she recalled. “But then it became clear — because it’s rather more complicated in our trial.”

That complexity has led uncertainty to swirl around one of the front-runners along with Pfizer Inc. and Moderna Inc. in the race for a shot to end the pandemic. Questions about the most effective dose of the vaccine, its safety record and the partners’ approach to testing it have cast doubt on whether the U.S. Food and Drug Administration will clear it.

Early Monday, AstraZeneca and Oxford reported results after 131 trial participants in the U.K. and Brazil contracted Covid 19. The average efficacy of 70% prevention sounded good, within the expectations of analysts and above a 50% standard the FDA had set for Covid vaccines.

The study also found 16 severe cases, all of them among people who didn’t get AstraZeneca’s shot, according to Moncef Slaoui, the former GlaxoSmithKline Plc researcher who heads up the U.S.’s Operation Warp Speed program. It was good news for Astra’s vaccine program that had been halted for six weeks in the U.S. while regulators reviewed a serious adverse event that the company never gave details on. Oxford will report details of those adverse events in its efficacy study that it will submit for review in the coming weeks.