The trials affected by the event include the phase 3 ENSEMBLE trial for JNJ-78436735


J&J temporarily paused its Covid-19 vaccine trials. (Credit: Nikopoley/

Johnson & Johnson (J&J) has temporarily paused further dosing in all its Covid-19 vaccine candidate clinical trials, following an unexplained illness in one of the participants.

The Covid-19 vaccine trials of the company that have been paused include the phase 3 ENSEMBLE trial for JNJ-78436735, which was initiated last month.

Johnson & Johnson said that the illness of the study participant is being reviewed and assessed by the ENSEMBLE independent Data Safety Monitoring Board (DSMB) and also the internal clinical and safety physicians of the company.

The company did not divulge the details of the illness of the participant adding that the individual’s privacy must be respected. Johnson & Johnson further indicated that the company is learning more about the illness and will gather all the facts before disclosing additional information.

The JNJ-78436735 vaccine candidate was developed by the company’s subsidiary Janssen Pharmaceutical Companies against Covid-19. Its phase 3 trial is aiming to enrol up to 60,000 volunteers, which has now been stopped temporarily due to the unexpected incident.

According to the healthcare firm, illnesses, accidents, and other adverse events, even those that are serious, are expected to be part of any clinical study, particularly large studies.

Johnson & Johnson stated: “Based on our strong commitment to safety, all clinical studies conducted by the Janssen Pharmaceutical Companies of Johnson & Johnson have prespecified guidelines.

“These ensure our studies may be paused if an unexpected serious adverse event (SAE) that might be related to a vaccine or study drug is reported, so there can be a careful review of all of the medical information before deciding whether to restart the study.”

More SAEs possible in the Covid-19 vaccine trials due to a large number of participants, says J&J

The company said that as serious adverse events are not unusual in clinical trials, their frequency can be expected to increase reasonably in studies involving large numbers of people. Furthermore, Johnson & Johnson said that as several clinical trials are placebo-controlled, it is not always possible to know immediately if a participant was administered a study treatment or a placebo.

Earlier this month, Janssen Pharmaceutical secured a deal with the European Commission to deliver up to 400 million doses of its Covid-19 vaccine candidate to the European Union member states.