The US is preparing to roll out the first doses of a COVID-19 vaccine on Monday with Pfizer and BioNTech's newly authorised jabs leaving in trucks from Michigan to reach states a day later.
The shipments of Pfizer's vaccine will start the largest mass vaccination effort in US history.
Health care workers and nursing home residents are first in line to receive the vaccine after the US Food and Drug Administration (FDA) gave the green light for its emergency use on Friday.
Three million initial doses are expected to be sent out as hospitalisations and deaths soar in the US.
Federal officials say the first shipments of Pfizer’s vaccine will be staggered, arriving in 145 distribution centres Monday.
An an additional 425 sites will get shipments Tuesday, and the remaining 66 sites will receive the vaccines on Wednesday.
The vaccine, co-developed by German partner BioNTech, is being given out based on each state's adult population.
Pennsylvania health care 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 Saturday. "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 Pfizer/BioNTech vaccine will be sent to hospitals and sites that can store it properly. It's being shipped with dry ice and GPS sensors to ensure the shipments stay cold.
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 jab a few weeks later.
The vaccine is based on new mRNA technology that gives genetic instructions for the body to make the coronavirus' spike protein. This triggers the immune system to make antibodies.
While the vaccine was determined to be safe, regulators in the UK are investigating several severe allergic reactions.
The FDA’s instructions tell providers not give it to those with a known history of severe allergic reactions to any of its ingredients.
Another vaccine by Moderna will be reviewed by an expert panel this week and soon afterward could be allowed for public use.