Researchers at Oxford University said on Thursday they have developed a method to predict the efficacy of new Covid-19 vaccines based on a blood test, potentially offering a short-cut around massive clinical trials that are increasingly difficult to conduct.

The researchers looked at the concentration of a range of virus-fighting antibodies in the blood of trial participants after they had received the vaccine developed by AstraZeneca and Oxford University, now known as Vaxzevria.

By looking at which of those trial volunteers later contracted symptomatic Covid-19 and which did not, the researchers came up with a model...