Drugs that can keep high-risk COVID-19 patients out of the hospital are going begging because the supposed breakthrough treatments require an hour-long intravenous infusion and offer a rather small chance of benefit.

On Monday, Regeneron announced results that may help make its monoclonal antibody combination, now branded REGEN-COV, more useful. The drug combo was given in a single shot and dramatically reduced the chance of infection in unvaccinated individuals living with someone newly diagnosed with COVID-19.

To be sure, vaccination is the most effective, durable way to prevent the disease and curb the pandemic. But monoclonal antibodies might be a backup for people who refuse to be immunized, or immune-compromised people who may not be adequately protected by vaccination.

Regeneron’s news release said it will ask U.S. regulators to expand REGEN-COV’s emergency authorization so it can be given as a shot for preventive purposes in “appropriate populations.” It is currently authorized for nonhospitalized COVID-19 patients who are at high risk of severe disease because of obesity, diabetes, kidney disease, or other chronic conditions.

“If authorized, convenient [shot] administration of REGEN-COV could help control outbreaks in high-risk settings where individuals have not yet been vaccinated, including individual households and group living settings,” said University of North Carolina infectious disease specialist Myron Cohen, a leader of the federally sponsored COVID Prevention Network.

Also on Monday, Regeneron shared results from a trial aimed at expanding use of REGEN-COV to infected people who have no symptoms and are thus a major source of transmission. The drug, given as a shot, reduced the risk of progressing from asymptomatic to symptomatic infection by almost a third over 29 days.

“These data pave the way for REGEN-COV to be used before patients become symptomatic,” trial coleader Katharine Bar, an infectious disease specialist at the Hospital of the University of Pennsylvania, said in the news release.

Patients do not pay for monoclonal antibodies — at least, not directly — but the government has heavily invested in these drugs, which mimic the body’s natural disease-fighting antibodies. Eli Lilly contracted to provide 100 million doses of its drug, called bamlanivimab. Regeneron in January promised to provide 1.25 million more doses of casirivimab and imdevimab by the end of June, a deal worth $2.62 billion — or more than $2,000 a dose.

In the clinical trials that led to authorization, the Lilly and Regeneron therapies significantly reduced the chance of hospitalization or death. However, even high-risk people are unlikely to get that sick. In Regeneron’s trial, 3% of patients on the antibodies were hospitalized or went to the emergency room, compared to 9% of patients on a placebo. In the Lilly study, 1.6% on the drug were hospitalized vs. 6.3% on placebo.

Another obstacle for lab-made antibodies is the short window of opportunity. The drugs should be given within 72 hours of a positive COVID-19 test, before the infection outruns the power of antibodies.

Regeneron’s latest data are based on a clinical trial of 1,500 people with negative COVID-19 tests who were living with someone who had tested positive for COVID-19 within four days.

During the first week of the trial, infection spread to 1.2% who got REGEN-COV, vs. 4.3% who got a placebo — a 72% risk reduction. After a month, the placebo group’s infection rate rose to 7.8%, while it barely budged to 1.5% for the treated group — an 81% risk reduction.

Those who developed COVID-19 despite antibody therapy had about a 90% reduction in symptoms and virus levels compared to placebo recipients who got sick.

Whether demand for monoclonal antibodies will catch up to the vast supply remains to be seen. The Infectious Diseases Society of America currently recommends the use of Lilly’s to keep high-risk patients out of the hospital, while saying Regeneron’s versions “may have similar clinical benefit, but data are more limited.”

Many hospitals and the federal government are trying to increase use of the drugs by making infusions easier to access, and raising awareness among doctors and patients. Federal officials created an online treatment locator for patients.

The University of Pittsburgh Medical Center has set up 15 antibody infusion centers across Pennsylvania and one in New York. It also reaches out to eligible patients to offer the treatment.

“I think this [Regeneron announcement] is exciting,” said infectious disease physician Ryan Bariola, who coleads UPMC’s infusion program. “It looks like another step forward, assuming it pans out.”