U.S. Regulators have authorized the emergency use of the first experimental antibody drug for COVID-19 in patients who are not hospitalized but are at risk of serious illness because of their age or other conditions. The Food and Drug Administration (FDA) granted emergency use authorization (EUA) to Eli Lilly & Co’s LLY.N bamlanivimab based on trial data showing that a one-time infusion of the treatment reduced the need for hospitalization or emergency room visits in high-risk COVID-19 patients. The White House, in an emailed statement, hailed the FDA’s decision as “a major milestone.”

The FDA said Lilly’s antibody can be used for anyone over the age of 65 who is recently diagnosed with mild-to-moderate COVID-19 and for patients age 12 and older who have an underlying health condition putting them at risk for serious illness. The clearance gives doctors an option for tackling the virus in high-risk patients before they’re sick enough to require hospitalization. Other treatments that received the regulatory go-ahead, such as convalescent plasma, a component collected from the blood of recovered Covid patients containing immune factors, and Gilead Sciences Inc.’s antiviral Remdesivir are intended for use in severely ill Covid-19 patients.

Experimental antibody treatments could become a powerful component of the arsenal that doctors use to treat the Coronavirus. Anthony Fauci, the top U.S. infectious-disease official, has referred to antibody-based medicines as a bridge to a vaccine.