An unusual experiment to prevent nursing home staff members and residents from infection with the coronavirus has succeeded, the drug maker Eli Lilly announced on Thursday.
A drug containing monoclonal antibodies — laboratory-grown virus-fighters — prevented symptomatic infections in residents who were exposed to the virus, even the frail older people who are most vulnerable, according to preliminary results of a study conducted in partnership with the National Institutes of Health.
The researchers found an 80 percent reduction in infections among residents who got the drug, compared with those who got a placebo, and a 60 percent reduction among the staff, results that were highly statistically powerful, Eli Lilly said.
The data have not yet been peer-reviewed or published. The company expects to present the findings at a future medical meeting and to publish them in a peer-reviewed journal, but did not say when.
The study included 965 participants at nursing homes: 666 staff members and 299 residents. (The company had hoped more residents would participate, but it proved difficult to enroll them; many had dementia, and others were leery of getting an intravenous drug.)
There were four deaths from Covid-19 among study participants. All were among nursing home residents who got a placebo, not the drug.
The drug, bamlanivimab, already has an emergency use authorization from the Food and Drug Administration that allows Eli Lilly to provide it to symptomatic patients early in the course of their infection.
But this study asked if the drug could stop infections before they started. It was an unusual experiment: In trucks equipped with mobile labs, medical staff sped to nursing homes the moment a single infection was detected there. As soon as the workers arrived, they set up temporary infusion centers to administer the drug.
The research ended this weekend with an emergency meeting of the data safety and monitoring board, an independent group monitoring the incoming results. The data were strong and convincing enough to call a halt to the placebos.
“My jaw dropped when I saw the table of outcomes,” said Dr. Myron Cohen, a professor of medicine at the University of North Carolina at Chapel Hill, and a principal investigator who helped design and implement the study.
Although the study has ended, Dr. Daniel Skovronsky, Eli Lilly’s chief scientific officer, said the company would continue to rush to nursing homes in its study network when an outbreak is detected. “Everyone will get the drug,” he said.
Experts who were not part of the study were enthusiastic, but emphasized that they had not yet seen complete data. “I see only positives here,” said Dr. Ofer Levy, director of the precision vaccine program at Boston Children’s Hospital. “This is a win.”
Dr. Kathleen Neuzil, director of the Center for Vaccine Development and Global Health at the University of Maryland, also was encouraged.
“The mortality effect is remarkable,” she said, adding that the drug should be used more widely to prevent and treat Covid-19, “particularly in populations such as nursing home residents, who have high mortality and may have suboptimal responses to vaccines.”
Vaccines, of course, also protect people from infection with the virus, and nursing home staff and residents were among the first group prioritized for the shots. But supplies are inadequate, and many nursing home workers, afraid of the vaccines, have declined to get them.
And following vaccination, it can take six weeks for the body to produce enough antibodies for maximum protection, said Dr. Srilatha Edupuganti, a vaccine researcher at Emory University in Atlanta and a study investigator.
The monoclonal antibody treatment, she said, can give nearly equivalent protection immediately, although it will not last as long as the protection offered by a vaccine.
Eli Lilly plans to approach the F.D.A. about an emergency use authorization for use of the drug to prevent infections in frail older populations, especially those in nursing homes or long-term care facilities, Dr. Skovronsky said.