Lilly has paused enrollment in its ACTIV-3 study evaluating the antiviral drug Remdesivir plus an experimental antibody therapy being developed by Lilly in patients hospitalized with COVID-19. According to the company, independent monitors paused the study out of an abundance of caution.

Study pauses are not uncommon in clinical trials and are often resolved.

The trial began in August and aims to enroll 10,000 hospitalized COVID-19 patients in the U.S., Denmark and Singapore. Trial participants are given remdesivir, which is authorized in the U.S. as an emergency treatment for COVID-19, plus either the Lilly antibody or a placebo. The main goals are reducing the need for extra oxygen and time to recovery.

The ACTIV-3 clinical trial is the only ongoing study evaluating the efficacy of Lilly’s neutralizing antibody in hospitalized COVID-19 patients, the most advanced stage of the disease. The dose of bamlanivimab being investigated in this trial is 7000 mg.

Individuals in the ACTIV-3 study have been infected with the virus for a longer period of time and may have more severe symptoms than patients studied in other bamlanivimab trials. Hospitalized patients receive different treatments for COVID-19 than earlier stage patients, including treatment with the antiviral medicine remdesivir.

For these reasons, hospitalized patients may have less benefit from neutralizing antibodies, which are a supplement to the patients’ own immune system, as they may have developed their own endogenous antibody response and be in a phase of disease characterized by inflammatory responses to virus. This is why the use of immunosuppressive treatments is both widespread and still being investigated in hospitalized patients.