Johnson & Johnson is temporarily pausing dosing in all its COVID-19 vaccine candidate clinical trials, including the Phase 3 ENSEMBLE trial, which was detailed in a press release last month as a potentially "pivotal" global effort that would build on the successes of positive interim results from prior phases.

In a statement shared on Monday, a rep said that the company remains "committed to providing transparent updates" throughout the clinical development process, which is why it decided to release an extended explanation on the decision to hit the proverbial pause button.

In that statement, the reason given for the temporary halt is the discovery of an "unexplained illness" in one of the study participants. Additional information regarding the nature of that illness is not included in the statement, though the rep confirms the illness in question is currently under review and evaluation by the ENSEMBLE Data Safety Monitoring Board. Internal clinical and safety physicians are also assisting in the review.

Given the size of the study, and the nature of such studies in general, events like this are traditionally expected from those involved. "We must respect this participant's privacy," the rep added. "We're also learning more about this participant's illness, and it's important to have all the facts before we share additional information."

Additionally, CNBC reported that spokeswoman Molly McCully stated, “Safety is of the utmost importance to Lilly. We are aware that, out of an abundance of caution, the ACTIV-3 independent data safety monitoring board (DSMB) has recommended a pause in enrollment. Lilly is supportive of the decision by the independent (Data Safety Monitoring Board) to cautiously ensure the safety of the patients participating in this study.”

To be clear, there's a major difference in a clinical trial being hit with a "study pause" and a "regulatory hold." While the former sees the study sponsor choosing—based on their own safety protocols—to temporarily pause dosing and/or recruitment procedures, the latter is ignited by a regulatory agency (i.e. the FDA).