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Lilly Covid-19 antibody treatment trial paused. Experts say that's normal

The Lilly drug is being tested in patients hospitalized with Covid-19.

Drugmaker Eli Lilly and Co. said Tuesday that the clinical trial of its Covid-19 antibody treatment has been paused because of a potential safety concern.

"Out of an abundance of caution, the ACTIV-3 independent data safety monitoring board (DSMB) has recommended a pause in enrollment," Lilly spokeswoman Molly McCully said in an emailed statement to NBC News. "Lilly is supportive of the decision by the independent DSMB to cautiously ensure the safety of the patients participating in this study."

The Lilly drug, called LY-CoV555, is similar to the Regeneron antibody treatment President Donald Trump received after his Covid-19 diagnosis. It is currently being tested in hospitalized patients.

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The pause in the Lilly trial comes a day after Johnson & Johnson paused its Covid-19 vaccine trial after a volunteer had an unexplained illness. J&J said the participant's condition was being reviewed and evaluated by the Data Safety Monitoring Board. It's unclear whether the volunteer who had an adverse event had received the actual vaccine or a placebo.

It's not uncommon for late-stage trials to hit bumps, said Dr. Eric Topol, director of the Scripps Research Translational Institute in California. "[I'm] not too concerned, pending details."

Dr. Carlos del Rio, infectious diseases expert at Emory University School of Medicine, agreed. "Pauses are not infrequent in a clinical trial, and in these studies, they are going to be probably a bit more frequent as the development line for a product is significantly truncated,” he said.

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Just last week, Lilly requested emergency use authorization from the Food and Drug Administration for the antibody treatment, using data from a separate clinical trial — not the trial that was just paused.

No published or peer-reviewed results have been released about the treatment, but last month the company released partial results from a trial of the drug, which suggested it could help keep patients with mild to moderate forms of the illness from progressing to a point where they would need to be hospitalized.

The paused trial is sponsored by the National Institute of Allergy and Infectious Diseases, part of the National Institutes of Health. When the phase 3 trial was announced in August, Lilly had planned to enroll approximately 300 volunteers hospitalized with mild to moderate illness with fewer than 13 days of symptoms, according to the NIH. Participants were also given the antiviral remdesivir.