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expert reaction to pausing of Oxford vaccine trial due to participant falling ill

It has been reported that the University of Oxford and AstraZeneca COVID-19 human vaccine trial has been halted due to a participant falling ill.


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

“This is a standard procedure in clinical research in response to detecting a serious event.

“It gives the study team and the independent advisory board time to evaluate the details of the event and to decide the causal association between the vaccine and the event. The key objectives are to assess the risks for those who have already been vaccinated and, as a precaution, to protect people who are due to be vaccinated.

“There were no serious adverse reactions in the phase 1/2 study of this vaccine, which was published in The Lancet in July. The study included 1,077 vaccinees who were observed for eight weeks. This appears to be the first serious event with this vaccine.

“There are unconfirmed reports about the specific nature of the condition. But we need to hear from the study team themselves, once they have fully investigated the matter, before we can assess the impact of this event on the development of the Oxford vaccine.”


Dr Ohid Yaqub, Senior Lecturer at the SPRU (Science Policy Research Unit), University of Sussex, said:

“A suspension such as this is not unusual for phase 3 trials, which have tens of thousands of participants.

“Suspending the trial gives time to investigate whether the incident is related to the vaccine or is happening by coincidence. If the data and safety monitoring board decides it’s the latter, the trial will resume. Other trials will also investigate their data too.

“In some senses, it is good that such a routine event is being publicised because it helps to build trust as it provides an opportunity for people to see the procedures at work. But there is a balance to be struck with respect to how much detail is released as a running commentary about the trial so far, because it may bias the results. Those details will be released at the end of the trial.“


Dr Charlie Weller, Head of Vaccines Programme at Wellcome, said:

“Safety is the most important consideration when developing any vaccine, and it is right for the trial to be paused while an investigation takes place. This is often a normal part of the process in vaccine trials, which involve tens of thousands of people. It’s critical to quickly understand whether the illness has any relationship to the vaccine or the placebo and to share data openly, as Oxford University and AstraZeneca have done.

“Vaccines are among the most rigorously tested and monitored products we have in society, and the COVID-19 vaccines should be no different. We welcome the news that nine vaccine developers have pledged to uphold scientific and ethical standards for these vaccines and prioritise safety.

“Today’s news reminds us of the importance of funding and developing a wide range of vaccine candidates, alongside treatments and testing. We don’t yet know which will be successful, but ensuring all advances are fairly available globally is our only exit from this pandemic.”


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

“When large numbers of people are included in trials, coincidental events can occur and when they are unexpected, then an investigation is required to see if they are just coincidence or a result of the vaccine.

“While it was not in a trial, in September 2009 a young woman died shortly after receiving an HPV vaccine. Some people immediately claimed it was because the cheaper of two available vaccines had been used. The relevant batch of vaccines was immediately quarantined (in some senses equivalent to pausing a trial), but after a post-mortem it was shown that the cause of death was a very rare large malignant tumour in her chest. The HPV vaccine was in no way responsible.

“We do not know what event has occurred, but given that in the UK those aged over 70 have been included in the trials, coincidental events are to be expected. Very occasionally, what might be expected in an older person, such as a stroke (and this is certainly not a suggestion that it is such an event that has happened here), can occur in a young person.

“The whole way of conducting vaccine trials with independent data and safety monitoring boards, as well as regulatory processes, is intended to protect the participants in the trials and is why trials are conducted. This very incident shows that the Oxford trial, and any other trials conducted in the UK, are monitored very carefully and precautions are taken to protect both the trial participants and those who might get the vaccine in the future.

“It is premature to speculate on whether the vaccine caused the adverse event, and even if it eventually is concluded that it is possible the vaccine was the cause, there may be other factors involved and it would not necessarily mean the vaccine could not be used at all. It may be possible to identify factors which would suggest the vaccine can be used safely in some people but, as a precaution, not in others. One has to remember that in the situation of a large number of cases of illness from the virus, the vaccine might be preventing a large number of deaths so that the balance of benefit and harm is tipped a long way in favour of benefit.”


Prof Ian Jones, Professor of Virology, University of Reading, said:

“An inevitable consequence of testing a vaccine on large numbers of people is that some will naturally fall ill of other causes during the trial. A similar incident some ten years ago during the roll out of the HPV vaccine resulted in the immediate quarantine of a batch of the vaccine, although the overall programme was not suspended. We must wait and see what the investigation in this case shows but at the moment, I think unfortunate more than sinister would be the best description of the halt.”


Dr Doug Brown, Chief Executive of the British Society for Immunology, said:

“Vaccines can prevent illness and save lives, but it is also vital that they are thoroughly tested before being rolled out on a wide scale to ensure they are safe to use. Because safety is so critical, vaccine trials are incredibly complex, and each vaccine goes through many stages of testing both in the lab and in clinical trials. All vaccine clinical trials have numerous strict safety procedures in place to monitor the health of participants.

“What we are seeing with the news that the AstraZeneca–Oxford University COVID-19 vaccine trial has been paused due to ill health in one participant is one of these safety procedures kicking in. As we all know, people fall ill for a multitude of reasons, and the project team will now be reviewing in depth what is the cause of this person’s illness and whether it is linked to having been given the vaccine or not. To be ultra-cautious, the trial is paused while this process is carried out – this is another of the safety procedures built-in to all vaccine trials. We will have to await the findings of this review to find out more, but it’s worth highlighting that this type of pause to a vaccine trial to investigate an unexplained illness is not an uncommon event, and in fact it’s exactly what we should all want to see the vaccine researchers doing to ensure the safety of any potential vaccine above everything else.

“However, this news does provide a good illustration of why conducting thorough and robust vaccine trials is so critical, and is just one more reason why we must not put pressure on researchers to rush through a vaccine for widespread use before these large and complex trials have been carried out.”


Dr James Gill, Honorary Clinical Lecturer, Warwick Medical School, and Locum GP, said:

“During the development of any drug, people will develop side effects – hence we know ibuprofen can cause heart burn. People will also fall ill during the natural course of their lives whilst they have taken the vaccine – we know that the ‘flu vaccine doesn’t cause ‘flu but some people can be unlucky and catch a bug around the time they are inoculated.

“It is crucial that we remember correlation – i.e. things happening at the same time – does not mean causation – i.e. the two things happening can be coincidental.

“The fact that the AstraZenca and Oxford developed vaccine trial has been temporarily paused should be paradoxically considered a good thing

“Whilst it has been reported that one trial volunteer has become ill, this may be due to an issue related to the vaccine. It also may not. That the trial has announced this, and has placed a pause on the testing to allow an independent panel to look into the event, should be championed as good science and great transparency for the public who are waiting for news on a COVID-19 vaccine

“Personally, I would be suspicious of a vaccine for a novel virus which was developed without any hiccoughs or pauses. Science on TV is great, and usually gets completed in the course of an episode. In a real lab, chemistry, patients and biology don’t often follow a nice simple course, which is why from the start scientists have said that this COVID vaccine development will take considerable time to get right and safe.”


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


Declared interests

Prof Saad Shakir: “No conflicts to declare.”

Dr Ohid Yaqub: “No conflicts to declare.”

Dr Charlie Weller: “No conflicts of interest.”

Prof Stephen Evans: “No conflicts of interest. I am funded (one day per 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 on any grants obtained from them. I am the statistician to the ‘meta-Data Safety and Monitoring Board’ for CEPI. I am paid for my attendance at those meetings and will be paid expenses for travel if that occurs.”

Prof Ian Jones: “No conflicts of interest.”

Dr Doug Brown: “Dr Doug Brown is a trustee of the Association of Medical Research Charities (AMRC).”

None others received.

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