The federal health regulator said Tuesday that GlaxoSmithKline’s IV drug for COVID-19 should no longer be used because it may not be effective against a subvariant of omicron that now accounts for the majority of cases in the United States.

The U.S. Food and Drug Administration announced that the company’s antibody drug, sotrovimab, is no longer authorized to treat patients in any U.S. state or territory. The decision was expected, as the FDA has repeatedly restricted the drug’s use in the Northeast and elsewhere as the BA.2 version of omicron has become dominant.

BA.2 accounted for 72 percent of COVID-19 cases sequenced by health authorities, the Centers for Disease Control and Prevention said Tuesday. Some experts have warned that the BA.2-driven surge is similar to what has hit European countries, although the number of cases in the United States has yet to rise.

The drug from GlaxoSmithKline and co-developer Vir Biotechnology is the latest antibody drug to be used as a byproduct of a mutated coronavirus, after it made Eli Lilly and Regeneron’s drugs obsolete. The FDA revoked their authorization in January after deciding they were ineffective against the original version of omicron.

The decision leaves doctors and hospitals with only one antibody still authorized for routine COVID-19 cases: a different Eli Lilly drug that the regulator said appeared to be effective against BA.2.

Doctors can also prescribe antiviral pills that are unaffected by omicron mutations that primarily affect the virus’s signature spike protein. Pfizer and Merck have mostly shipped their pills to chain pharmacies and medical clinics, hoping to get them into the hands of patients as soon as possible so they can work.

Since last fall, the federal government has purchased nearly $2 billion worth of GlaxoSmithKline drugs and shipped more than 900,000 doses to U.S. states.

London-based GlaxoSmithKline said last month it was studying higher doses of the anti-BA.2 antibody.But the FDA needs to review and approve the company’s request before it can resume use in the U.S.

Antibody drugs are lab-made versions of virus-blocking proteins found in the human body. Each antibody is formulated to attack a specific invader — such as a virus or bacteria — but as the coronavirus mutates repeatedly, the drug needs to be reformulated.

The drugs are prescribed for people who have recently contracted COVID-19 and are at increased risk of serious illness or death, including older adults or people with diabetes, heart disease and other common health problems.