Dr Anthony Fauci, the US’s leading expert in infectious diseases, said on Sunday it should be known by the end of November or early December if a vaccine was safe and effective.

Fauci was asked on the BBC’s Andrew Marr Show if Donald Trump’s claims that a Covid-19 vaccine, while not a guarantee, would be coming by the end of the year were true.

"We will know whether a vaccine is safe and effective by the end of November, the beginning of December," he replied. “The question is, once you have a safe and effective vaccine, or more than one, how can you get it to the people who need it as quickly as possible?

“The amount of doses that will be available in December will not certainly be enough to vaccinate everybody. You’ll have to wait several months into 2021. "

Healthcare workers are likely to be given priority access to any vaccine, as well as people whose underlying health means they are considered at increased risk of complications if they get Covid-19.

“That could start by the end of this year, the beginning of January, February, March of next year. When you talk about vaccinating a substantial proportion of the population, so that you can have a significant impact on the dynamics of the outbreak, that very likely will not be in to the second or third quarter ”, Fauci added.