As we mentioned earlier, the Trump administration has indicated it will not be joining a WHO-backed coalition of 172 countries to share equitably any future vaccines against Covid-19 – and this has got some experts worried.

The Coalition for Epidemic Preparedness Innovations (CEPI) is one of the organisations supporting the initiative, called Covax, which plans to buy and distribute fairly some two billion doses of any vaccine in 2021.

Richard Hatchett, who heads CEPI, told the AFP news agency he is worried that the US, as well as other rich nations, are already reserving the first doses for themselves – at the expense of other countries.

"What we need to persuade global leaders is that as a vaccine becomes available in these initially limited quantities, it needs to be shared globally, that it shouldn't be the case that just a handful of countries get all of the vaccine that is available in the first half of 2021," he said.

The Trump administration said on Tuesday it would "continue to engage our international partners to ensure we defeat this virus". But it has signed contracts guaranteeing at least 800 million doses from six manufacturers which, Hatchett said, puts the US "potentially in a situation of oversupply if all of the vaccines that they've invested in are successful".