WASHINGTON — U.S. health regulators on Friday authorized a new antibody drug that targets the omicron variant, a key step in restocking the nation’s arsenal against the latest version of COVID-19.

The Food and Drug Administration said it cleared the Eli Lilly drug for adults and adolescent patients with mild-to-moderate cases of COVID-19. Lilly announced work on the treatment late last year after testing revealed that its previous antibody therapy was ineffective against the dominant omicron variant.

U.S. health regulators on Friday authorized bebtelovimab, the new antibody drug from Eli Lilly that specifically targets the omicron variant of COVID-19. Eli Lilly and Company via AP

The Biden administration had purchased 600,000 doses before the authorization and will begin shipping initial supplies to state health authorities for distribution.

It’s “an important step in meeting the need for more tools to treat patients as new variants of the virus continue to emerge,” said Dr. Patricia Cavazzoni, FDA’s drug center director.

The FDA announcement comes after the two leading monoclonal antibody treatments in the U.S. turned out to be ineffective against omicron. Data indicate the Lilly drug also works against the emerging BA.2 mutation of omicron.

Lilly said the contract for its new drug – bebtelovimab, pronounced “beb-teh-LO-vi-mab” – is worth at least $720 million.

Laboratory-made monoclonal antibodies stand in for the human body’s immune system by acting to block an invading virus. Delivered by IV or by injection, the medicines are meant to be used early in an infection.

But late last month the FDA revoked its emergency use authorization for Regeneron’s antibody drug, along with Lilly’s. The two medications had been the the backbone of antibody treatment, and doctors were hard pressed to come up with fallbacks when they didn’t work against omicron.

Alternate therapies, including antiviral pills from Pfizer and Merck, have been in short supply. An antibody drug from GlaxoSmithKline that remains effective against omicron is also scarce.

Scientists say COVID-19 treatments like monoclonal antibodies are not a substitute for vaccination.

Under the U.S. contract with Lilly, the government will receive about 300,000 treatment courses of the new antibody drug in February and another 300,000 in March.