A top executive at AstraZeneca pushed back on 25 November against criticism that the company failed to disclose enough data from a clinical trial of its Covid-19 vaccine earlier this week, and acknowledged scepticism about the vaccine’s 90% effectiveness in a group of patients who were accidentally given a lower dose than intended.

“I’m not going to pretend it’s not an interesting result, because it is—but I definitely don’t understand it and I don’t think any of us do,” said Mene Pangalos, AstraZeneca’s executive vice president for biopharmaceuticals research and development. “It was surprising to us.”