Drugmaker Eli Lilly has paused a US government-sponsored clinical trial of its Covid-19 antibody treatment has been paused because of a safety concern.
The drug is similar to the Regeneron Pharmaceuticals treatment President Donald Trump received after he contracted Covid-19.
"Out of an abundance of caution, the ACTIV-3 independent data safety monitoring board (DSMB) has recommended a pause in enrolment," an Eli Lilly spokeperson said.
"Lilly is supportive of the decision by the independent DSMB to cautiously ensure the safety of the patients participating in this study."
Lilly had already asked US regulators to authorise its antibody therapy, LY-CoV555, for emergency use after publishing data in September showing it helped cut hospitalization and emergency room visits for COVID-19 patients.
The treatment is being developed with Canadian biotech AbCellera.
Safety panel reviews illness that led to J&J vaccine trial pause
Johnson & Johnson said it would take at least a few days for an independent safety panel to evaluate an unexplained illness of a study participant that led to a pause in the company's Covid-19 vaccine trial.
Rival AstraZeneca's US trial for its coronavirus vaccine candidate - which uses a similar technology - has remained on hold for more than a month after a participant in the company's UK trial fell ill.
J&J said the illness was being reviewed by an independent data and safety monitoring board as well as by its own clinical and safety team.
The data board, which is also reviewing AstraZeneca's US trial, is required to submit its findings to the US Food and Drug Administration before the study can be restarted.
Mathai Mammen, head of research & development at J&J's drugs business, said it would be "a few days at minimum for the right set of information to be gathered and evaluated".
He said because the study is blinded, the company did not yet know if the ill person had been given the vaccine or a placebo. Mammen added that J&J remains on track to complete recruitment for its 60,000-person trial in the next two to three months.
The company said such pauses are not unusual in large trials.
It noted that the voluntary "study pause" in giving doses of the vaccine candidate to trial participants was different from a "regulatory hold" imposed by health authorities.
J&J has said it expects to have enough data to apply for US regulatory clearance by the end of the year. Pfizer Inc and Moderna Inc have said they expect to be able to apply for FDA clearance for their vaccine candidates even sooner.
Health experts have voiced concerns that U.S. President Donald Trump could put pressure on the FDA and drugmakers to rush an unsafe vaccine to market to bolster his re-election prospect. He has repeatedly said a vaccine could be available prior to the Nov. 3 election.
AstraZeneca last month paused late-stage trials of its experimental coronavirus vaccine developed with the University of Oxford due to a serious unexplained illness in a British study participant. While AstraZeneca's trials in Britain, Brazil, South Africa and India have since resumed, its US trial remains on hold.
The J&J and AstraZeneca vaccines both use modified, harmless - although different - versions of adenoviruses to deliver genetic instructions to human cells in order to spur an immune response to the target virus, in this case the novel coronavirus.