Dr Moncef Slaoui, the chief adviser for the White House vaccine programme, has said that it was "extremely unlikely but not impossible" that a vaccine could be available by the end of next month.
In an interview with National Public Radio, Dr Slaoui, the chief scientific adviser of the Trump administration's coronavirus vaccine and treatment initiative, called Operation Warp Speed, explained that the Centres for Disease Control and Prevention's (CDC) guidance to states to prepare for a vaccine as early as late Octobera notification Dr Slaoui said he had learnt of through the news mediawas "the right thing to do" in case a vaccine was ready by that time.
"It would be irresponsible not to be ready if that was the case," he said. However, he described that as a "very, very low chance".
That message ran counter to the optimistic assertions in recent days from the White House that a vaccine could be ready for distribution before election day on Nov 3.
At the Republican National Convention, President Donald Trump said a vaccine could be ready "before the end of the year or maybe even sooner".
US VP Mike Pence said yesterday that the Trump administration would not "cut corners" in making a vaccine for the coronavirus available, although it wants to move as fast as possible to deliver something that is safe and effective.
"We're not going to cut corners in the development of a vaccine, but at the same time, through Operation Warp Speed, the president has made it clear that we want a safe and effective vaccine available for the American people absolutely as soon as is possible to have," Mr Pence told Fox Business Network.
Dr Slaoui confirmed that both main candidates, referred to as Vaccine A and Vaccine B, were being developed by Pfizer and Moderna.
He stated that there was "no intent" to introduce a vaccine before clinical trials were completed, and that trials would be completed only when an independent safety monitoring board, separate from the government, affirmed the effectiveness of the vaccine.
The interviewer, Ms Mary Louise Kelly, raised the timing of a possible vaccine given in the documents that the CDC recently sent to public health officials, and asked directly whether the delivery of the vaccine was being motivated by political concerns.
"For us, there is absolutely nothing to do with politics," Dr Slaoui responded, stating that those involved were working as hard as they could because so several people were dying every day.
Though he continued to express doubt that a vaccine would be ready by the end of next month, Dr Slaoui said, "I firmly believe that we will have a vaccine available before the end of the year, and it will be available in quantities that can immunise patients, subjects at the highest risk", including the elderly and those who are working in jobs with high exposure to the virus.
He estimated there would be enough vaccine by the end of the year to immunise "probably between 20 (million) and 25 million people". He stated that manufacturing would be ramped up so that there would be enough doses for the United States' population "by the middle of 2021".
The World Health Organization (WHO) doesn't expect widespread vaccinations against Covid-19 until the middle of next year, a spokesman said yesterday, stressing the importance of rigorous checks on their effectiveness and safety.
None of the candidate vaccines in advanced clinical trials so far has demonstrated a "clear signal" of efficacy at the level of at least 50 per cent sought by the WHO, spokesman Margaret Harris said.
NYTIMES, REUTERS