The first Americans to receive a Covid-19 vaccine could get it as soon as 11 December, according to the head of the US coronavirus vaccine programme.
Dr Moncef Slaoui told US network CNN the plan was to "ship vaccines to the immunisation sites within 24 hours" of a vaccine being approved.
The comments come amid a surge in coronavirus cases across the country.
The US has recorded more than 12m cases and 255,000 deaths, according to data compiled by Johns Hopkins University.
These are the highest tolls registered anywhere in the world.
American pharmaceutical company Pfizer and its partner BioNTech submitted an application on Friday for emergency authorisation in the US of their Covid-19 vaccine.
Data from an advanced trial showed the vaccine protects 94% of adults over 65.
Pfizer hopes to produce up to 50 million doses in 2020 and up to 1.3 billion doses in 2021. Each person needs two doses.
A Food and Drug Administration (FDA) vaccine advisory committee is set to meet on 10 December to discuss whether to authorise the vaccine.
Dr Slaoui said the vaccine could be rolled out "maybe on day two after approval, on the 11th or the 12th of December".
He said the vaccine would be distributed based on each state's population. States will be responsible for deciding who gets the vaccine first, but it is recommended that priority be given to those most at risk, like front-line workers and the elderly.
Dr Slaoui said that by May, the country could achieve "herd immunity" with 70% of the population vaccinated.
US officials earlier granted emergency authorisation for an experimental antibody treatment, developed by Regeneron, given to President Donald Trump after his Covid-19 diagnosis.
Also on Sunday, G20 leaders said they would "spare no effort" to ensure the fair distribution of coronavirus vaccines worldwide.