Two Major COVID Clinical Trials Were Paused Over Safety Concerns — Which Is Exactly How Trials Should Work

Trials for Eli Lilly’s antibody treatment and Johnson & Johnson’s COVID-19 vaccine were both paused this week.

Within 24 hours, two pharmaceutical companies separately confirmed that their COVID-19 clinical trials — one for a vaccine, the other for a therapy — were being paused over potential safety concerns.

A government-sponsored trial for Eli Lilly’s antibody drug was paused due to a “potential safety concern,” according to emails sent to testing sites on Tuesday. The company confirmed in a statement that an independent board overseeing the trial’s safety had made the decision “out of an abundance of caution.” Eli Lilly’s therapy is similar to another experimental treatment manufactured by Regeneron and used to treat President Donald Trump two weeks ago.

And on Monday, Johnson & Johnson confirmed that it paused its vaccine trial due to “an unexplained illness in a study participant,” as first reported by Stat.

There was little information immediately available about either incident, including whether they were linked to the pharmaceutical being tested or the placebos it was being tested against, or when the trials might be restarted. Johnson & Johnson said in a statement that it was “learning more about this participant’s illness, and it’s important to have all the facts before we share additional information.”

Study pauses, which are initiated by companies, are not uncommon occurrences in trials and are less severe than clinical holds, which are initiated by regulators. And “adverse” events — illnesses or other undesirable medical outcomes — are expected to some degree in all clinical trials, especially ones that involve large numbers of patients. Johnson & Johnson noted that it typically does not “communicate study pauses publicly,” but added that it proactively discloses any regulator-required holds.

Still, some medical experts have criticized pharmaceutical companies for not being more transparent about issues that could seem troubling to a lay audience, given the tremendous degree of interest in vaccines and treatments for COVID-19 and the importance of maintaining public trust.

As of yet, there is no vaccine or FDA-approved therapy for a virus that has killed more than 210,000 Americans. The back-to-back pauses of two high-profile COVID-19–related trials raise the possibility that they could be delayed.

Eli Lilly's trial, which is sponsored by the National Institute of Allergy and Infectious Diseases, tested the antibody therapy on 300 patients hospitalized with mild to moderate COVID-19 who also received an antiviral drug, remdesivir, commonly used to treat these patients.

In a statement, a NIAID spokesperson said the trial was paused when the safety board found that the trial had reached a notable difference in safety outcomes between the treatment group and the placebo group. It is not yet clear which group may have experienced the safety issue described, or whether the trial had met the threshold for "futility," where researchers can conclude that the pharmaceutical does not work.

As a result, the independent safety board "recommended pausing enrollment out of an abundance of caution and continuing data collection and follow-up of current participants for safety and efficacy," the statement said. The board will review the data again on Oct. 26 before deciding whether or not to resume the trial.

Both Eli Lilly and Regeneron filed for emergency authorization from the FDA last week in the middle of a publicity storm spurred by Trump. Last week, the president referred to Regeneron’s antibody cocktail — which he received in addition to the antiviral drug remdesivir and the steroid dexamethasone — as “a cure.”

According to a summary of results released last month from another Eli Lilly trial studying more than 450 patients recently diagnosed with a mild to moderate case of the disease, volunteers receiving the antibody treatment had a 72% lower risk of hospitalizations and emergency room admissions, compared to those taking the placebo.

Late last month, Johnson & Johnson began testing its one-shot vaccine in a late-stage clinical trial with up to 60,000 participants. It is one of the manufacturers backed by Operation Warp Speed, the public-private partnership that is channeling $10 billion into COVID-19 vaccines and therapies, including about $1.5 billion to Johnson & Johnson.

These weren’t the first COVID-19–related trials to be paused. AstraZeneca has halted its vaccine clinical trial at least twice to investigate two cases of severe illness developed by participants. The first patient, in July, was deemed to have multiple sclerosis, unrelated to the vaccine. A second person in September developed neurological symptoms consistent with a rare but serious condition called transverse myelitis, according to news reports.

AstraZeneca’s trial has since resumed in the UK, Brazil, South Africa, and India but is still on hold in the US pending the FDA’s review.

Trump has also made statements about how quickly pharmaceutical companies will be able to develop a vaccine, despite concerns from scientists who say that the process should not be rushed and adequate safety data should be collected.


This story has been updated to include a statement from the National Institute of Allergy and Infectious Diseases.

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