(Bloomberg) -- US regulators said Wednesday that Eli Lilly & Co.’s monoclonal antibody treatment for Covid-19 is no longer authorized for emergency use because it’s not likely to work against infections caused by the forms of omicron that are dominant across the country. 

The Food and Drug Administration warned earlier this month that Lilly’s drug bebtelovimab was unlikely to work against omicron subvariants BQ.1 and BQ.1.1 that were starting to gain ground across the US. Those mutations have since grown to account for more than 57% of Covid infections throughout the country, according to Centers for Disease Control and Prevention data.

“As we have seen over the last several months, prevalence of Covid variant sublineages vary by state, region and even country, and can change rapidly,” a Lilly spokesperson said in an email. “Based on pseudovirus data, Lilly can confirm that bebtelovimab does not retain neutralization activity against the BQ.1 and BQ.1.1 variants.”

Lilly shares closed Wednesday up nearly 2% after the FDA announcement. The stock has rallied more than 34% for the year to date.

Lilly’s bebtelovimab was one of only two remaining antibody drugs left in the US after earlier mutations knocked others made by GSK Plc and Vir Biotechnology, as well as Regeneron Pharmaceuticals Inc., off the market. Lilly said it will continue to search for potential monoclonal antibody candidates for clinical development against new variants.

During an earnings call earlier this month, Lilly’s Chief Scientific Officer Daniel Skovronsky said the company has potentially broadly neutralizing antibodies in its labs that it would consider bringing forward “if there is a need and an aligned path forward with health authorities.” But in the same call, executives said that antibodies will not be a major driver of long-term growth for Lilly. 

That leaves AstraZeneca Plc’s Evusheld, which helps prevent infections, as the only antibody drug available in the US for doctors to give their patients. However, that could soon change. Omicron subvariants including BQ.1 and BQ.1.1 are likely also resistant to Evusheld, according to the National Institute of Health’s Covid-19 Treatment Guidelines Panel. The NIH panel said on Nov. 10 that the decision to administer Astra’s treatment “should be based on the regional prevalence of the resistant subvariants, the individual patient’s risks, the available resources, and logistics.” 

Antibody therapies have proven essential for treating and preventing disease in roughly 7 million immune-compromised Americans for whom vaccines and antivirals can be less effective. Covid’s rapid mutations have been a challenge for companies in developing new antibody drugs, but the Biden administration recently asked Congress for $5 billion to support development of next-generation vaccines and therapeutics to fight future variants.

The FDA said in a statement that Lilly and its authorized distributors have paused commercial distribution of bebtelovimab until further notice by the agency and the Administration for Strategic Preparedness and Response has paused the fulfillment of any pending requests. However, federal regulators are still recommending that all product be retained in the event that Covid variants susceptible to bebtelovimab again become more prevalent in the future.

(Updates with additional context, statement from Lilly starting in second paragraph.)

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