(Reuters) - AstraZeneca will supply up to half a million extra doses of its experimental antibody-based COVID-19 combination therapy to the United States, in a bright spot for the company after more governments suspended use of its vaccine over safety fears. The antibody therapy, which has yet to be approved by U.S. regulators, is designed to treat the disease rather than prevent it like the vaccine, which several countries have stopped using while reports of blood clots in some people are investigated. The Anglo-Swedish drugmaker said on Tuesday the $205 million U.S. 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, London-listed AstraZeneca said, adding that the new agreement is contingent on an emergency use approval by the U.S. 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. While AstraZeneca has undergone a rollercoaster ride with its COVID-19 vaccine, it has been working on developing new treatments and repurposing its existing drugs to prevent and treat coronavirus infections. Monoclonal antibodies, such as the ones being used in AZD7442, are synthetically manufactured copies of the human body’s natural infection-fighting proteins, and are already being used to treat some types of cancers. A series of issues have bogged down the drugmaker’s vaccine rollout: including pauses in trials, questions over the most effective dosing, and supply problems. Share gains from optimism around the cheap and easy-to-ship shot have also been decimated. On Tuesday, the stock was up 1.5% at 7,090 pence in early trading. At its peak in July last year, the company hit 10,120 pence.