The company said the cocktail of two types of antibodies, initially discovered by Vanderbilt University Medical Center, reduced by 77% the risk of developing symptomatic COVID-19, the potentially deadly disease caused by the coronavirus.
More than 75% of the participants had chronic conditions, including some linked to a diminished immune response to vaccination, it said.
The results mark a change of fortune for the drugmaker, which reported in June that a smaller late-stage trial failed to provide evidence that the antibody cocktail, known for now as AZD7442, protected people who had contact with an infected person from the disease.
The Anglo-Swedish drugmaker, which has faced challenges with the rollout of its COVID-19 vaccine, is also working on repurposing existing drugs to fight the virus.