The deal includes supplies of a retooled Omicron-adapted vaccine, pending regulatory clearance, according to Pfizer.
Drugmakers have been developing vaccines to target the Omicron variant that became dominant last winter.
The average price per dose in the new deal is over US$30, a more than 50% increase from the US$19.50 per dose the US government paid in its initial contract with Pfizer.
Some of the vaccine earmarked for adults included in the contract will be in single-dose vials, which are more expensive to manufacture but reduce waste of unused shots from open vials.
“We look forward to taking delivery of these new variant-specific vaccines and working with state and local health departments, pharmacies, healthcare providers, federally qualified health centres, and other partners to make them available in communities around the country this fall,” US Health and Human Services (HHS) official Dawn O’Connell said in a statement.
Advisers to the US Food and Drug Administration on Tuesday recommended a change in the design of Covid-19 booster shots for this fall in order to combat more recently circulating variants of the coronavirus.
The US government also has the option to purchase up to 195 million additional doses, bringing the total number of potential doses to 300 million, the companies said.
The new contract should boost 2022 vaccine sales for Pfizer and BioNTech, which share profits from the shots.
Pfizer has forecast Covid-19 vaccine sales of US$32 billion this year.
Analysts, on average, have forecast 2022 sales of around US$33.6 billion for the shots.
The US government has distributed close to 450 million doses of the Pfizer-BioNTech vaccine in the US since it was first authorised in December 2020, according to data from the US Centers for Disease Control and Prevention.
Over 350 million of those doses have been administered.
Because the Biden administration was unable to line up more Covid-19 funding from Congress earlier this month, it was forced to reallocate US$10 billion of existing funding to pay for additional vaccines and treatments.
According to HHS, the money to pay for doses in this new contract comes from that funding.