I hope it does not prove to be a major set-back. I was told last week that the vaccine would be ready by the end of September if governments were prepared to give the green light without the 30 000 volunteers. Maybe not very likely now but they have always said they could be ready in September.
Health Secretary Matt Hancock told Sky News' Kay Burley programme the pause is not necessarily cause for concern and that it has already overcome one such delay.
"It is obviously a challenge to this particular vaccine," he says.
"It's not actually the first time it has happened to the Oxford vaccine and it's a standard process in clinical trials."
Asked if it is a setback, Mr Hancock replied: "Not necessarily, it depends on what they find when they do the investigation. There was a pause earlier in the summer and that was resolved without a problem."
The nature of the adverse reaction and when it happened are not currently known. Clinical holds usually mean there is a pause in recruiting new participants and dosing current ones.
It is not uncommon for trials to be put on hold, but scientists are under pressure to develop a vaccine to help curb the pandemic.
Most serious adverse reactions that occur after vaccination are not related to the injection and are coincidental health problems, the World Health Organisation (WHO) has said.
When a vaccine is given to a large number of people, it is likely that a few people will experience a medical problem around the time of vaccination - but this does not prove any cause and effect.
Even so, researchers will need to investigate if there is any link.
Isn't there a risk of a serious adverse reaction in any medication that is taken?This is a normal procedure in a trial. The same process happened with the Hydroxychloriquine trials which were paused and have since restarted as the data was investigated and turned out to be false.
Trials often have safety concerns- and due to the rigorous nature of research they look for them and react accordingly for the safety of the trial participants.
When you are actively looking for adverse effects in a population of 2000 people you will find them across a long enough time period, just got to clarify if it is important, and secondly if it is a recurring theme.
No mention of a serious adverse reactionThis is an adverse event. Wether it is an adverse reaction is unknown. That is why investigations take place. Something has happened to someone on the trial and those running the trial have to find out if it was due to the vaccine.
Isn't there a risk of a serious adverse reaction in any medication that is taken?
There is always the caveat that 1 in so many may get xyz