Eli Lilly And Co.’s monoclonal antibody therapy bamlanivimab has received the FDA’s emergency use authorization to treat mild to moderate COVID-19 in patients age 12 years or older.

Lilly said it expects manufacturing as many as 1 million doses of bamlanivimab (LY-CoV555) by the end of this year. Worldwide distribution of the treatment, which is to be administered intravenously to individual patients as a single dose, is set to begin in early 2021. The U.S. government bought 300,000 doses and has said American patients will have no out-pocket costs though health care facilities may charge to administer the treatment.

The FDA authorization is based on Lilly’s phase II Blaze-1 study, a randomized, double blind, placebo-controlled investigation of outpatients with mild to moderate COVID-19. Viral load limits were reduced, according to the data, along with rates of symptoms and hospitalization.

The authorization comes with limitations. Bamlanivimab is not for patients hospitalized with COVID-19 or those requiring oxygen therapy because the therapy has yet to be proven beneficial for those groups. Matter of fact, the FDA continued, monoclonal antibodies “may be associated with worse clinical outcomes” when administered to hospitalized COVID-19 patients needing high flow oxygen or mechanical ventilation. The FDA also warned about hypersensitivity that includes anaphylaxis and infusion-related reactions in patients.

Lilly also noted that treatment benefits have yet to be found in hospitalized COVID-19 patients. Regeneron Pharmaceuticals Inc. hit the same wall when it paused recruitment in its study of monoclonal antibody REGN-COV2 of patients on high-flow oxygen and on mechanical ventilators.

To receive Lilly’s treatment, patients must test positive through direct SARS-CoV-2 viral testing, they must weigh at least 88 pounds and be at a high risk to progressing to severe COVID-19 or hospitalization or both. Even those at higher risk, such as those age 65 or older or those with certain chronic medical conditions, are approved for the treatment.

The process has been fraught for patients and Lilly. On Oct. 27, the NIH’s National Institute of Allergy and Infectious Diseases halted tests of bamlanivimab in hospitalized patients. Lilly continues to test bamlanivimab in Blaze-1 and Blaze-2, a study evaluating its use for the prevention of COVID-19 in residents and staff at long-term care facilities. In addition, bamlanivimab is being tested in the NIH-led ACTIV-2 study of ambulatory COVID-19 patients. Overall, about 1,000 trial participants have been dosed with bamlanivimab alone or in combination with a second Lilly antibody, etesevimab (LY-CoV016).

Lilly stock (NYSE:LLY) rose 3.5% in premarket trading.