The study assessed whether the therapy, a cocktail of two types of antibodies, could prevent adults who had been exposed to the virus in the past eight days from developing Covid-19 symptoms.
The Phase III study, which has not been peer reviewed, included 1,121 participants in the United Kingdom and the United States.
The vast majority, though not all, were free of the virus at the start of the trial.
Five more trials are ongoing, testing the antibody cocktail as treatment or in prevention.
The next one will likely be from a larger trial testing the product in people with a weakened immune system due to cancer or an organ transplant, who may not benefit from a vaccine.
AstraZeneca, Mene Pangalos
United Kingdom, United States