The Biden administration moved this week to stave off shortages of monoclonal antibodies, taking over distribution of the critical covid-19 therapy and purchasing 1.4 million additional doses.

The policy change that went into effect Monday is all but certain to result in cuts of the medication to some states, especially seven in the Deep South with high infection rates that have been using about 70 percent of the national supply.

Soaring demand for the therapy represents a sharp turn from just two months ago, when monoclonal antibodies were widely available and awareness of them was low. Consumers, doctors and states, amid little government promotion, were obtaining just a fraction of the available supply.

Since then, however, word of the highly effective therapy — which is free to patients — has spread, with federal officials and Republicans, including Florida Gov. Ron DeSantis, urging their use. Now the U.S. Department of Health and Human Services will, at least temporarily, set the rules for distribution of monoclonal antibodies instead of allowing states, medical facilities and doctors to order them directly.

“HHS will determine the amount of product each state and territory receives on a weekly basis,” an HHS spokesman said. “State and territorial health departments will subsequently identify sites that will receive product and how much.” The official spoke on the condition of anonymity to describe new procedures that are still being explained to communities throughout the country.

“This system will help maintain equitable distribution, both geographically and temporally, across the country, providing states and territories with consistent, fairly distributed supply over the coming weeks,” he added.

The move already has prompted concern in Alabama, where the president of the state medical association, Aruna Arora, said in a statement Monday that “Alabama’s hospitals are full and under tremendous stress. That’s why physicians are very concerned about federal efforts that will end up limiting our supply and access to this effective treatment.”

And in Florida, a spokeswoman for DeSantis said in a statement: “It is regrettable that the Biden administration would play politics with people’s lives during a pandemic, by withholding a life-saving treatment and providing mixed messages to Americans.” She was referring to President Biden’s vow last week to ramp up distribution of therapeutics for covid-19.

Alabama, Florida, Texas, Mississippi, Tennessee, Georgia and Louisiana — all states where the delta variant of the virus has been surging in recent months — have been using 70 percent of the monoclonal antibody supply in recent weeks, according to a person familiar with the situation. Other than Florida, those states have lower than average vaccination rates.

Late Tuesday, the government announced it had reached an agreement to buy another 1.4 million doses from the pharmaceutical company Regeneron for $2.9 billion, or $2,100 per dose. The company said it would start delivering the drugs within the week and supply the vast majority during the final three months of 2021.

In Texas, the Department of State Health Services alerted monoclonal antibody providers of HHS’s warning that “the national supply has considerably decreased and states should expect lower amounts of therapeutics available for shipment in the coming weeks,” according to Chris Van Deusen, a spokesman for the state health department.

In Tennessee, Bill Christian, a health department spokesman, said in an email that some people have been turned away because of delays in receiving shipments of the medication.

“HHS is reviewing all orders and as a result, facilities cannot anticipate shipments for scheduling patients. Instead, patients are being turned away, and appointments are canceled due to a lack of clarity on when treatment will be available,” Christian wrote.

In Mississippi, a state department of health spokeswoman said in an email that the state already allocates its medication based on how much each site is using and has enough on hand for now.

President Biden vowed in a speech last week to ramp up use of covid-19 therapeutics as part of a renewed effort to quell the pandemic in the United States. According to data from a meeting last week with stakeholders involved in monoclonal antibody distribution, 2.17 million doses of the therapy have been shipped to 8,003 sites and 938,000 have been used. The large difference between distribution and consumption may reflect a lag in reporting, according to one person tracking use of the medication.

Monoclonal antibodies are highly effective in preventing hospitalization among people with mild to moderate covid-19, the disease caused by the coronavirus, if given within seven to 10 days after symptoms appear. Administered via a half-hour infusion or four injections, the antibodies mimic the body’s own immune response to the coronavirus, moving quickly into action while the natural response is gearing up.

They also are available prophylactically for people who are unvaccinated or not fully vaccinated, have been exposed to the virus and are at higher risk for complications.

Under the new plan, the government will examine hospitalization data and case rates in states and territories, then determine how much they will receive each week. Each state then can set distribution of the medication to its own sites. A similar system was used last winter but abandoned when demand for the therapy remained low.

HHS also will limit supply to sites that have accounts with the government and can provide utilization data.

The government contracts with two companies, Regeneron and Eli Lilly, under emergency authorization from the Food and Drug Administration, to produce monoclonal antibodies that are distributed free to patients. Regeneron’s product is a cocktail of two monoclonal antibodies, casirivimab and imdevimab.

On Sept. 2, the FDA renewed authorization for Eli Lilly’s product, a combination of bamlanivimab and etesevimab, after pausing it in June to determine whether it is effective against the delta variant of the virus.

HHS already has previously bought more than 1.5 million doses from Regeneron, most of them at $2,100 per dose.

Regeneron spokeswoman Alexandra Bowie said it takes four to eight weeks to produce a batch of the medication and the company has ramped up production to try to meet the surge in demand.

A spokeswoman for Eli Lilly said in a statement that the company “continues to work with governments globally to help address the therapeutic needs of patients during the COVID-19 pandemic.”