WASHINGTON • The United States could be the first country to launch one of the most ambitious vaccine operations in history: distributing and administering up to 600 million doses of a Covid-19 vaccine in just a few months.

Massive vaccine campaigns are nothing new. But stamping out the coronavirus is a distinctly new challenge due to three factors: the short timeframe for inoculating a huge number of people, the fact that most vaccines will require two doses and the very low temperature at which some of the vaccines must be stored.

The vaccine developed by US pharmaceutical giant Pfizer and Germany's BioNTech, on track to be the first authorised for use in the US, must be stored at minus 70 deg C, while the flu vaccine can be kept in a normal refrigerator.

Pfizer vaccines distributed in the US will come from its largest manufacturing plant in Kalamazoo, Michigan, and their ship-out will include a precise, clockwork dance of containers, trucks and planes.

Thermal shipping containers will each be filled with dry ice and 975 vials of the vaccine, which each contain five doses, for a total of 4,875 doses. Every day, six trucks will take the doses to air carriers, such as FedEx, UPS and DHL, which will deliver them across the country in one to two days and across the globe in three, Pfizer said.

The firm expects an average of 20 daily cargo flights worldwide.

FedEx had to obtain special permission from civil aviation authorities to transport so much dry ice, which could pose a danger to the crew should it accidentally undergo "sublimation" and pass from a solid to a gas, it said.

Once the boxes reach their final destination, they can be opened briefly just two times a day.

"To run a large mass vaccination clinic, it's fine," said Dr Julie Swann, a pandemic response expert at North Carolina State University. But the vaccine would not be suitable for distribution at doctors' offices or pharmacies, which are too small, she warned.

At least in the beginning, Americans will have to go to hospitals or maybe even large distribution centres set up in parking lots much like Covid-19 test sites, she said. The vaccines can remain in their boxes for two weeks, meaning hospitals will not need a special freezer.

"We're not recommending at this time that hospitals or clinics purchase ultra-cold equipment," said Dr Janell Routh of the Centres for Disease Control and Prevention.

US biotech giant Moderna is also manufacturing a vaccine - which can be stored at minus 20 deg C, the temperature of a normal freezer.

The US government is organising a free distribution of this vaccine to US states and territories, with each jurisdiction to decide how to distribute the doses.

"The federal government does not intend, with very, very few exceptions, to touch a single dose of vaccine before it goes into the arm of Americans," said Operation Warp Speed official Paul Mango.

The objective is to offer vaccines to the most vulnerable populations before the end of next month, to healthcare workers before the end of January, and to all Americans by the beginning of April.

Pfizer expects to produce 50 million doses this year and 1.3 billion next year.

The US has already ordered 100 million in total, including 20 million to 30 million for delivery before the end of next month. The European Union has ordered 200 million, Japan 120 million, Britain 30 million and Canada 20 million.

DHL estimates that 15 million cooling boxes would need to be delivered over the next two years, with approximately 15,000 flights needed worldwide.

Poorer countries which lack storage capacity for large quantities of vaccines that need super-cold storage have little hope of benefiting from the first doses, said Dr Prashant Yadav, an expert in global health supply chains at the Centre for Global Development. Ultra-cold freezers that can reach temperatures of minus 80 deg C cost five times more than standard freezers and are made to order only, he added.

The US reported a record 201,214 daily Covid-19 cases on Tuesday, data from Johns Hopkins University showed, taking the tally to more than 10.2 million cases. The country has registered more than 239,000 deaths from the disease.

Over the past 10 days, about one million new coronavirus infections have been registered in the US, the fastest pace since it reported its first case in January.

AGENCE FRANCE-PRESSE, XINHUA