The National Institutes of Health (NIH) Tuesday paused enrollment in the late-stage clinical trial for Eli Lilly’s COVID-19 antibody treatment. The pause came on recommendation from the independent Data and Safety Monitoring Board (DSMB), which cited safety concerns.

The trial, sponsored by the NIH’s National Institute of Allergy and Infectious Diseases, is part of the NIH’s ACTIV-3 trial to test the experimental antibody treatment on COVID-19 patients who have already been hospitalized.

An NIH spokesperson told The New York Times that patients who had received the antibodies showed a different “clinical status” than those who received the placebo.

According to The Times, the guidelines for the trial include two “stopping rules,” or issues that would require the trial to be paused. One is “futility,” meaning the treatment is proven to have a low chance of working. The trial also can be stopped if patients in one group are faring worse than those in the other.

In a statement, the drug maker said:

“Lilly trusts the judgment of the independent DSMB and supports its decisions to exercise caution in ensuring the safety of the patients participating in this study.

“Importantly, the DSMB also considered the impact of the ACTIV-3 study pause on ACTIV-2 and did not recommend any changes to that study’s design or enrollment.”

This isn’t the first time a government agency has raised concerns about the Eli Lilly antibody trial. In November, the U.S. Food and Drug Administration (FDA) cited quality control issues at the manufacturing plant producing the experimental antibody treatment.

According to Reuters, the FDA classified the problems as the most serious level of violation, resulting in an “Official Action Indicated” notice. That means the “violations are serious enough and have a significant enough impact on the public health that something needs to be fixed,” a former associate counsel at the FDA told Reuters.

In an interview with MSNBC, Bill Gates, whose foundation is partnering with Eli Lilly to distribute the treatment to low and middle income countries, said he hopes this safety pause doesn’t “hold back the product.”

The Eli Lilly pause comes just one day after Johnson & Johnson halted its COVID-19 vaccine trials. A participant in that trial suffered what is believed to be an adverse reaction, but the specific illness has yet to be made public.

Jeremy Loffredo is a reporter for Children’s Health Defense.