Scientists are working on a benchmark for Covid-19 vaccine efficacy that would allow drugmakers to conduct smaller, speedier human trials to get them to market and address a huge global vaccine shortage.

Researchers are trying to determine just what level of Covid-19 antibodies a vaccine must produce to provide protection against the illness. Regulators already use such benchmarks - known as correlates of protection - to evaluate flu vaccines without requiring large, lengthy clinical trials.

"You could use it to predict efficacy from a vaccine, which will be more important as we are less able to conduct placebo-controlled trials," said Stanley Plotkin, inventor of the Rubella vaccine and an expert on correlates of protection.

"The information is flowing in," he said. "By the end of this year, I think there will be enough data to convince everyone...