AstraZeneca’s monoclonal antibody cocktail, AZD7442, failed to prevent symptomatic COVID-19 infection in a late-stage study of individuals recently exposed to the SARS-CoV-2 virus.

In the 1,121-participant phase 3 trial, a single dose of AZD7442 reduced the risk of developing symptomatic COVID-19 by 33 percent when compared against placebo, but the response was not deemed statistically significant.

AZD7442 combines two antibodies, tixagevimab and cilgavimab, derived from convalescent COVID-19 patients. The antibodies are meant to bind to the SARS-CoV-2 spike protein and mimic the body’s natural disease-fighting antibodies.

The findings mark a serious setback for AstraZeneca, which has agreements totaling $726 million to supply the U.S. government with up to 700,000 AZD7442 doses this year, pending FDA authorization or approval. The payments are contingent on approval or authorization.