Read: AstraZeneca advances COVID-19 antibody combo

Under that deal, announced in October, the U.S. invested $486 million for the development and supply of 100,000 doses of AZD7442, with an option to acquire up to an additional one million doses in 2021.

AstraZeneca has a separate agreement to supply the DoD with 100,000 doses, bringing potential U.S. supplies of the treatment to 700,000 doses in 2021, and the total value of current agreements with the U.S. government to $726 million.

Read: Germany and France become latest countries to halt use of AstraZeneca COVID-19 vaccine over blood clot concerns

Shares in FTSE 100-listed AstraZeneca AZN, +3.64%, which are down 1.83% so far this year, rose 3.06% in early morning trading in London.

AstraZeneca Chief Executive Pascal Soriot said the long-acting antibody combination has the potential to offer “almost immediate protection” to those who are not able to be vaccinated, to both prevent infection or treat the disease in patients already infected with the virus.

“The U.S. government’s support is critical in helping accelerate the development of AZD7442, which we believe will be an important tool in the fight against COVID-19,” Soriot said.

His comments come a day after several European countries suspended the rollout of AstraZeneca’s vaccine over reports of possible side effects, including several incidents of blood clots in individuals who had received the vaccine, which was developed with researchers at the University of Oxford.

AstraZeneca, the World Health Organization, and the European Medicines Agency have all said the vaccine is safe, and that there is no link between the shot and reported blood clots.

AZD7442 — a combination of two monoclonal antibodies (mAbs) — is currently being evaluated for the prevention and treatment of COVID-19 in late-stage trials in more than 9,000 participants around the world.

Other drug manufacturers are also developing antibody treatments aimed at reducing the severity of coronavirus disease among patients diagnosed with the infection.

Read: Vir Biotechnology shares surge after COVID-19 antibody drug shown to reduce risk of death

Last week, Vir Biotechnology VIR, +5.01% and GlaxoSmithKline GSK, +1.34% said they planned to seek emergency-use authorization for their experimental COVID-19 antibody therapy, after interim data from a study showed 85% reduction in hospitalization and deaths among patients.

If authorized, the treatment would add to the antibody drugs available, after those developed by Eli Lilly LLY, +0.41% and Regeneron REGN, +0.61% were given emergency-use authorization in November.

AstraZeneca said on Tuesday that it doesn’t expect its agreement to supply up to 500,000 additional doses of AZD7442 to the U.S. to affect its financial guidance for 2021.

Morgan Stanley MS, -1.72% said in a research note in December that AstraZeneca’s long-acting COVID-19 antibody cocktail could boost 2021 earnings by 30%, with positive data potentially being published early this year.

The new agreement is contingent on the treatment receiving emergency-use authorization from the U.S. Food and Drug Administration, AstraZeneca said.

Read: AstraZeneca sold its stake in Moderna for more than $1 billion, as it looks to develop its own pipeline of drugs

In a separate announcement, AstraZeneca said it completed the divestment of its 26.7% take in Viela Bio VIE, -1.03%, as part of the proposed acquisition of Viela by Horizon Therapeutics HZNP, -2.54%  for $775 million.