The National Institutes of Health researchers who initially halted the trial due to a safety concern, however, didn’t find that the treatment caused any harm, which may bode well for a regulatory review of the antibody’s use in a different setting.

While the decision to end the NIH-sponsored trial means Lilly’s antibody treatment may not work for the most extreme cases, other trials are ongoing to determine whether it helps patients earlier in the disease’s course. Notably, the finding that there wasn’t a safety issue in the hospital trial could remove a potential roadblock to emergency authorization that Lilly is seeking for using the antibody in patients outside of the hospital.

On Oct. 13, an independent data-safety monitoring board for the so-called ACTIV-3 trial sponsored by the National Institute of Allergy and Infectious Diseases, part of the NIH, recommended the study be paused due to a safety concern. The board has since found no difference in safety risks between the groups of patients receiving the antibody, known as LY-CoV555, and those who didn’t.

That means there is no longer a possibility that the hospital trial had unearthed an unexpected safety problem that could spill over into non-hospitalized patients, where the antibody has shown promising results.

Antibody therapies are being developed by a handful of companies, including Regeneron Pharmaceuticals Inc., AstraZeneca Plc, GlaxoSmithKline Plc and its partner Vir Biotechnology Inc., and are seen as a bridge to a coronavirus vaccine. The class of drugs has come into the spotlight as President Donald Trump received Regeneron’s experimental antibody therapy to treat his bout of Covid-19. Regeneron also approached U.S. regulators earlier this month for an emergency use authorization.

ACTIV-3 was testing a high-dose version of the antibody treatment Lilly is developing with Canadian biotech AbCellera Biologics Inc. in combination with the antiviral drug remdesivir, yet there was no indication it was effective, leading an independent panel to recommend stopping enrollment. The study signed up a total of 326 participants who were hospitalized with Covid-19.

In contrast to the hospital trial results, a company-sponsored trial with patients with less-severe cases of Covid-19, taking lower doses of LY-CoV555, produced promising early results in September. That became the basis of an approach to U.S. regulators for an emergency use authorization for those deemed “high risk” with mild-to-moderate Covid-19.

The announcement is an indication that monoclonal antibodies may only work if given early in the course of a coronavirus infection, before the virus has had a chance to penetrate deep into the lungs and cause serious damage.

Clinical studies of the experimental antibody therapy in the outpatient setting, as well as a preventive treatment in nursing homes, have continued unaffected. The independent data-safety monitoring board overseeing ACTIV-3 didn’t recommend any changes to another government-run trial, known as ACTIV-2.

The Indianapolis-based drug giant said in a statement Monday that it remains confident LY-CoV555 may prevent progression of disease. Lilly executives are expected to give an update on its experimental antibody program on Tuesday morning as the company reports third-quarter earnings.

Lilly is currently in talks with Operation Warp Speed for supply, Chief Executive Officer David Ricks told Bloomberg earlier in the month.