The first shipments of Covid-19 vaccine left on trucks and planes early yesterday, kicking off a historic effort to stop a surging pandemic that is claiming more than 2,400 lives a day in the US.
Mask-wearing workers at a Pfizer factory in Michigan began packing the first shipments of the vaccine developed with German partner BioNTech SE in dry ice shortly after 6:30am ET (1130 GMT) yesterday.
Trucks carrying pallets of boxed, refrigerated vaccine began rolling away from the Kalamazoo facility at 8.29am, escorted by body armour-clad security officers in a pickup truck and a SUV.
The shots then were loaded onto FedEx and United Parcel Service planes that will whisk the precious cargo across the country.
US hospitals are preparing for the first shots to go into arms today, but it will take months before most Americans can get a Covid-19 vaccine.
Healthcare workers and elderly residents of long-term care homes are first in line to receive the inoculations of a two-dose regimen given about three weeks apart.
More than 100mn people, or about 30% of the US population, could be immunised by the end of March, US Operation Warp Speed chief adviser Dr Moncef Slaoui said in an interview with Fox News yesterday.
That would still leave the country far short of herd immunity that would halt virus transmission, so masks and social distancing will be needed for months to control the rampaging outbreak.
Health officials will also have to overcome widespread hesitancy about the new vaccines, with many Americans concerned the record speed at which they were developed may have compromised safety.
Only 61% of US respondents said they are open to getting inoculated, a Reuters/Ipsos poll showed.
“It is however critical that most of the American people decide and accept to take the vaccine,” Slaoui said.”We are very concerned by the hesitancy that we see.”
The massive logistical effort is further complicated by the need to transport and store the Pfizer/BioNTech vaccine at -70C (-94), requiring enormous quantities of dry ice or specialised ultra-cold freezers.
Workers clapped and whistled as the first boxes headed to the trucks.
The long-awaited moment comes as the US death toll was approaching 300,000 and infections and hospitalisations set daily records.
Some models project that deaths could reach 500,000 before vaccines become widely available in the spring and summer.
Slaoui said the US hopes to have about 40mn doses of vaccine distributed by the end of December, which he said would include vaccines by both Pfizer and Moderna 
An outside FDA advisory panel is scheduled to consider the Moderna vaccine on Thursday, with emergency use expected to be granted shortly after.
Although the federal government is co-ordinating distribution efforts, states have the final say over who gets the first shots.
The federal government is sending the first shipments to more than 600 locations, as millions wait for the vaccine and a return to life free from the fear of the deadly illness.