US states are being told to get ready to distribute a potential COVID-19 vaccine by the start of November.
"CDC urgently requests your assistance in expediting applications for these distribution facilities," read a 27 August letter from Robert Redfield, director of the Centres for Disease Control and Prevention.
Dallas-based wholesaler McKesson Corp has a deal with the federal government to set up centres to distribute a coronavirus vaccine when it becomes available.
The CDC, "if necessary, asks that you consider waiving requirements that would prevent these facilities from becoming fully operational by November 1, 2020," two days before the US presidential election, said the letter.
The US Food and Drug Administration has raised the possibility that a vaccine might be given emergency approval before the end of trials designed to ensure its safety and effectiveness.
A woman in the US is given the first shot in the clinical trial of a potential vaccine for the COVID-19 coronavirus by a pharmacist. Source: AAP
A request for such extraordinary approval would have to come from the vaccine developer, FDA chief Stephen Hahn told the Financial Times in an interview published on the weekend.
The CDC provided states with documents giving details of a vaccine rollout plan, adding that vaccines would either be approved as licensed vaccines or under emergency use authorisation.
Recipients would probably require a second "booster" dose, according to the documents.
"Vaccine and ancillary supplies will be procured and distributed by the federal government at no cost to enrolled Covid-19 vaccination providers," the documents say.
Priority will be given to essential workers, national security officials, seniors and members of vulnerable racial and ethnic groups, according to The New York Times.
Three Western drug makers are progressing with their Phase 3 clinical trials, involving tens of thousands of participants.
The three are AstraZeneca, which is partnering with Oxford University in England; Moderna, collaborating with the US National Institutes of Health; and the Pfizer/BioNTech alliance.
By the nature of the trials, it is difficult to predict when reliable results will emerge.
Half of the participants in such trials receive an experimental vaccine, while the other half are given a placebo.
Under normal procedures, test administrators must wait - probably for months - to see whether there is a statistically significant difference in the infection rate of the two groups.
The US Food and Drug Administration however has raised the possibility that a vaccine might be given emergency approval before the end of trials.