AstraZeneca will supply up to half a million extra doses of its experimental antibody-based COVID-19 combination therapy to the US.

The antibody therapy, which has yet to be approved by US regulators, is designed to treat the disease rather than prevent it like the vaccine.

The drugmaker said the $205 million US extension for 500,000 antibody doses builds on a contract agreed with government agencies in October for initial supplies of 200,000 doses of the antibody cocktail, AZD7442.

The treatment is a combination of two monoclonal antibodies, AstraZeneca said, adding that the new agreement is contingent on an emergency use approval by the US Food and Drug Administration.

“The US Government’s support is critical in helping accelerate the development of AZD7442,” AstraZeneca Chief Executive Pascal Soriot said.

The total value of the deal now stands at $726 million for up to 700,000 doses. AZD7442 is being evaluated in late-stage trials, the company said, adding that it currently does not expect any changes to its 2021 forecasts due to the deal.