Johnson & Johnson COVID-19 Vaccine Trials Temporarily Paused Due to Unexplained Illness in Participant

Johnson & Johnson (New Brunswick, NJ, USA) has temporarily paused further dosing in all its COVID-19 vaccine candidate clinical trials, including the Phase 3 ENSEMBLE trial, due to an unexplained illness in a study participant.

In September, the company had announced the launch of its large-scale, pivotal, multi-country Phase 3 ENSEMBLE trial for its COVID-19 vaccine candidate, JNJ-78436735, being developed by its Janssen Pharmaceutical Companies. The initiation of the ENSEMBLE trial followed positive interim results from the company’s Phase 1/2a clinical study, which demonstrated that the safety profile and immunogenicity after a single vaccination were supportive of further development. ENSEMBLE aims to enroll up to 60,000 volunteers across three continents, and study the safety and efficacy of a single vaccine dose versus placebo in preventing COVID-19.


However, according to a statement released by the company, an unexplained illness in a study participant had forced it to temporarily pause further dosing in all its COVID-19 vaccine candidate clinical trials, including the Phase 3 ENSEMBLE trial. Johnson & Johnson has said that the participant’s illness was being reviewed and evaluated by the ENSEMBLE independent Data Safety Monitoring Board (DSMB) as well as its internal clinical and safety physicians.

The company said that pre-specified guidelines for all its clinical studies ensure that the studies may be paused if an unexpected serious adverse event (SAE) that might be related to a vaccine or study drug is reported, so that there can be a careful review of all of the medical information before deciding whether to restart the study. According to Johnson & Johnson, SAEs were not uncommon in clinical trials, and the number of SAEs can reasonably be expected to increase in trials involving large numbers of participants. The company has said that it was learning more about the participant’s illness and would be able to share additional information only after gathering all the facts.

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