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expert reaction to reports that Johnson & Johnson trial of COVID-19 vaccine has been paused due to illness in one participant

It has been reported that the pharmaceutical company Johnson & Johnson have paused the trial of their COVID-19 vaccine due to illness in one participant.


Prof Stephen Evans, Professor of Pharmacoepidemiology, London School of Hygiene & Tropical Medicine, said:

“Normally pauses in recruitment in a trial do not reach the public domain. The explanation on STAT News ( is clear on this.

“They are frequent where thousands of healthy people are given something new, notably a vaccine. It is more usual that this is a matter for the data and safety monitoring board (DSMB) and the trial steering committee (TSC). The TSC typically has investigators and some independent scientists involved. The DSMB is (meant to be) totally independent (and in my experience always is) and holds closed meetings where observers from the TSC or sponsors of the trial are excluded. It is not usually disclosed to the public- there is no gain in doing so and it is the DSMB that has the responsibility of ensuring that patients’ interests are paramount and also that the scientific integrity of the trial is maintained.

“The current situation of leaks of this type of data is perhaps understandable with the heightened interest around a potential COVID-19 vaccine but does not benefit patients or the reliability of the trials.

“If the DSMB concludes that it is possible that a serious type of adverse event should be under particular surveillance they will communicate this to all the investigators. In most instances, single adverse events are coincidental, especially when including large numbers of participants in trials, some of whom will be older and may have as yet undiagnosed problems that are nothing to do with the vaccine, but can appear when trial participants are seen regularly by health professionals, or the patients themselves become more attuned to their health while under surveillance.

“The fact that trials are paused should indicate that there should be confidence in the whole process of monitoring the safety of trial participants is working well.”


Prof Saad Shakir, Director of the Drug Safety Research Unit (DSRU), said:

“Serious adverse events are expected in a clinical trial that includes 60,000 vaccinees. While the independent Data Safety Monitoring Board (DSMB) will know, they can’t say whether the event occurred in a person who received the active vaccine or the comparator because divulging this will compromise the blinding of the study.

“In addition, it cannot announce the clinical details of the event for confidentiality reasons.

“The description of the event as an ‘unexplained illness’ is interesting and somewhat unusual. They are likely to be investigating its nature in detail, in collaboration with the doctors who are treating the patient. Given the description ‘unexplained illness’, an educated guess is that it could be an event that affected the nervous system, though this is by no means certain.

“While the monitoring board looks for causality when assessing serious adverse events, it is acknowledged that regulators or members of the DSMB may be forced to act even in the absence of a definite causal relationship. 

“We will have to wait for more details about this event to assess its impact on the development of this vaccine.” 



All our previous output on this subject can be seen at this weblink:


Declared interests

Prof Stephen Evans: “No conflicts of interest.  I am funded (1 day/week) by LSHTM.  They get funding from various companies, including Astra Zeneca and GSK but I am not funded by them, I have no involvement in obtaining funding from them and I am not an investigator or any grants obtained from them.  I am the statistician to the “meta-Data Safety and Monitoring Board” for CEPI.  I will probably be paid for my attendance at meetings and expenses for travel.”

Prof Saad Shakir: “The Drug Safety Research Unit is an independent charity (No. 327206), which works in association with the University of Portsmouth. It receives unconditional donations from pharmaceutical companies. The companies have no control on the conduct or the publication of the studies conducted by the DSRU. Saad Shakir is an employee of Drug Safety Research Unit, an independent charity (No. 327206), which works in association with the University of Portsmouth. He has no conflicts of interest to declare.”

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