Federal officials say the first shipments of Pfizer's vaccine will be staggered, arriving in 145 distribution centres tomorrow, with an additional 425 sites getting shipments on Wednesday, and the remaining 66 on Thursday.
The vaccine, co-developed by German partner BioNTech, is being doled out based on each state's adult population.
Pennsylvania healthcare giant UPMC has chosen staff who are critical to operating its facilities as among those getting the first round of vaccinations, said Dr Graham Snyder, who led the centre's vaccine task force.
"It's very exciting. I will be thrilled, that moment when we administer our first dose," Snyder said. "That will clearly be a watershed moment for us."
Snyder said the UPMC system estimates that half its employees are willing to get the vaccine as soon as it's offered to them.
The vaccine is heading to hospitals and other sites that can store it at extremely low temperatures of about -70C.
Pfizer is using containers with dry ice and GPS-enabled sensors to ensure each shipment stays colder than the weather in Antarctica.
Doses should be delivered to all vaccination sites identified by states, such as local pharmacies, within three weeks, federal officials said.
The rollout will ensure there is enough vaccine to give people the two doses needed for full protection against Covid-19. That means the government is holding back three million doses to give those vaccinated in the first round a second shot a few weeks later.
The Food and Drug Administration authorised emergency use of the vaccine, saying it is highly protective and presents no major safety issues. While US regulators worked for months to emphasise the rigor and independence of their review, they faced political pressure until the final stages.
Concerns that a shot was rushed out could undermine vaccination efforts in a country where some are sceptical about vaccines — some because of overall opposition to vaccines and others because of the quick timeframe in which the virus vaccines were developed.
Even some healthcare workers have said in surveys that they would forgo at least the first round of shots to see how things go.
The head of the FDA has repeatedly insisted that the agency's decision was based on science, not politics, despite a White House threat to fire him if the vaccine wasn't approved before Sunday.
- AP