The drug, called AZD7442, reduced the risk of developing severe COVID-19 or death by 50% in patients who had been symptomatic for seven days or less, meeting the main goal of the trial.
"An early intervention with our antibody can give a significant reduction in progression to severe disease, with continued protection for more than six months," said Mene Pangalos, executive vice president, biopharmaceuticals R&D at AstraZeneca.
The company will discuss the data with health authorities, it added, without elaborating.
AstraZeneca is also developing the drug cocktail as a therapy to protect people who do not have a strong enough immune response to COVID-19 vaccines. It requested emergency approval from US regulators for its use as a prevention drug last week.