Johnson & Johnson pauses COVID-19 vaccine trial after patient's 'unexplained illness'

The company says it is investigating before determining next steps in the COVID-19 vaccine trial.

Johnson & Johnson announced Monday that the company is pausing its phase 3 COVID-19 vaccine trial after a clinical trial participant contracted an "unexplained illness," the company said in a statement.

The pause in the closely watched trial, dubbed ENSEMBLE, was first reported by STAT News.

"We have temporarily paused further dosing in all our COVID-19 vaccine candidate clinical trials, including the Phase 3 ENSEMBLE trial, due to an unexplained illness in a study participant," the company statement read.

The company said that such outcomes are common in clinical trials, and stressed the difference between a study pause — which could be a short and only temporary occurence — and a regulatory hold, which is a formal action by the FDA that can mean much longer delays.

The company said it is undertaking a "careful review of all of the medical information before deciding whether to restart the study."

The ENSEMBLE trial began in late September, and is one of nearly a dozen phase 3 trials as pharmaceutical companies race to develop a COVID-19 vaccine, according to a tracking database published by the New York Times. ENSEMBLE involves more than 60,000 volunteer patients across three continents.

It is not the only COVID-19 vaccine trial that has had to halt investigations. In early sepetmber, the vaccine candidate from AstraZeneca and Oxford University paused for a "side effect" experienced by a patient. That trial resumed about a week later in the United Kingdom, but remains on hold in the United States.