WASHINGTON - US President Donald Trump said on Monday (Sept 7) that a coronavirus vaccine could be ready in October and vowed it would be "very safe and very effective".
This is a promise Mr Trump has made repeatedly.
But the American public remains deeply sceptical of the claim and many voters are mistrustful of a vaccine that would be rushed and made available this year, according to recent polls.
Concerns that development of a coronavirus vaccine in the United States is being expedited ahead of the presidential election in November are clouding its impending arrival, with the White House adding to the confusion by sending mixed messages about when a vaccine will be available.
The Centres for Disease Control and Prevention asked governors late last month (Aug 27) to be prepared for the distribution of a Covid-19 vaccine to healthcare workers and high priority groups as early as Nov 1, two days before Election Day.
The timeline has raised concerns that a vaccine is being hurried to boost Mr Trump's chances of re-election.
There is general consensus among public health experts and even top health officials that an October vaccine would be very unlikely.
US Surgeon General Jerome Adams said last week (Sept 4) that the Nov 1 deadline was a "just in case" scenario, adding that it was "possible, but not probable" that a vaccine would be ready early.
Three vaccine developers are currently in the third and final phase of trials, which involves large-scale testing on tens of thousands of people in safety and efficacy studies that typically take months to complete.
But the Food and Drug Administration (FDA) has the authority to end phase three trials early and authorise a vaccine if its trial results are overwhelmingly positive.
FDA chief Stephen Hahn told the Financial Times on Aug 30 that he was open to bypassing the normal approval process in this manner, although he stressed that the decision would be based on science, medicine and data, and not politics.
Public health experts are urging caution. In a Sept 3 essay in the Foreign Policy magazine, pandemic expert Laurie Garrett wrote that she had no confidence that a safe, effective vaccine would be ready for use by Halloween.
"The pace required here is astounding, dramatically more rapid than any prior drug or vaccine rollout in history. Though officials insist no corners are being cut, the timetable is simply too short for full safety analysis of any vaccine," she said.
Ms Garrett argued that drugmakers could not possibly guarantee the safety of their vaccine by October, as complications might not show up in a quick sampling of healthy adults.
"This is why vaccine clinical trials usually last for several months and involve far more volunteers than have been recruited for the Covid-19 product," she wrote.
Drugmakers are reportedly signing up to a pledge not to prematurely seek government approval of vaccines until they have met rigorous safety and efficacy standards.
But Americans remain wary.
Democratic vice-presidential candidate Kamala Harris said on Sunday that she would not take Mr Trump's word alone on the reliability of a vaccine.
"I will say that I would not trust Donald Trump and it would have to be a credible source of information that talks about the efficacy and the reliability of whatever he's talking about," she told CNN in an interview, remarks that Mr Trump later slammed as "anti-vaccine rhetoric".
A CBS-YouGov survey conducted between Sept 2 and Sept 4 found that scepticism over development of a safe vaccine this year had deepened in recent weeks.
Two-thirds of voters say that if a vaccine was announced this year, their first thought would be that it was rushed through, rather than viewing it as a scientific achievement. This attitude was more pronounced among Democrats and independent voters compared to Republicans.
Moreover, 21 per cent of voters say they would get a vaccine as soon as possible if one became available this year at no cost, down from 32 per cent in late July.
University of Texas at Austin political psychologist Bethany Albertson, who studies political attitudes, said that whether people believed a vaccine would happen by this year was highly dependent on voters' party affiliations.
Said Dr Albertson: "That's a message that will resonate with and reassure Republican voters. I don't expect that it's a message that will reassure Democrats.
"I think Democrats would need to actually see it happening, and the scope of that project seems far beyond Election Day."