The Food and Drug Administration has withdrawn emergency use authorization for AstraZeneca’s Covid-19 antibody cocktail Evusheld as the treatment is not expected to neutralize the currently dominant XBB.1.5 subvariant of omicron.
The FDA had limited Evusheld’s use earlier this month for the same reason and the agency’s Thursday announcement sent U.S. shares of London-based AstraZeneca down 1.31% to $65.75.
Omicron subvariant XBB.1.5 has been spreading rapidly in the country since December and it made up nearly half of all U.S. Covid cases last week, according to government data.
The FDA’s decision resonates with concerns raised by the European health regulator about the effectiveness of monoclonal antibodies such as Evusheld against newer variants.
AstraZeneca said it was informed that the agency will decide about reinstating authorization of Evusheld if the prevalence of resistant variants in the United States decreases to 90% or less on a sustained basis.
The drugmaker plans to continue to share relevant data with the FDA and other health authorities regarding Evusheld and SARS-CoV-2 variants.
Monoclonal antibodies act by binding to the spike protein on the surface of the SARS-CoV-2 virus, but the virus has been evolving, causing changes in this protein and affecting how the antibodies work against them.
In November, the U.S. health regulator also pulled emergency use authorization for Eli Lilly's Covid drug bebtelovimab, citing similar concerns.
Evusheld was first authorized in late 2021 by the FDA to prevent Covid infections in individuals with weak immune systems or a history of severe side effects from coronavirus vaccines.
Follow NBC HEALTH on Twitter & Facebook.