This is due to a very rare type of clotting problem with low platelet count resulting in cerebral venous thrombosis which can lead to a stroke and possibly death (this is not related to the much commoner clots in the legs or lungs). These clots can happen naturally but because they are so rare it is not clear how many would have occurred normally and how many are excessive and maybe caused by the vaccine.

The European drug information has now been listed to include this rare event as a possible side effect.

There has been a total of 79 reports in over 20 million doses of this vaccine given and out of those 19 deaths in UK.

This is an incredibly rare side effect - 4 per million with a 1 in a million chance of death – approx. the same as being murdered in the next month. It is very much rarer than most drug side effects, so it is extremely unlikely. There are many more of these clots seen in young pill takers for instance, yet we accept the risk for the benefits – and there are yet more cases if you become pregnant.

There is no direct causal link proven, merely at this stage an association. This means that with later evidence it might prove coincidental but given the possibility of a true link and the fact that this is a new vaccine with only very short experience, it was sensible to issue this advice pending further research and evidence.

The condition was seen more frequently in younger people and two thirds were young women, hence the advice to offer an alternative vaccine below the age of 30y.

Why have we been slower than other countries to make a change? This just demonstrates the difficulties in interpreting all the emerging data, which changes often daily as new analysis takes place. Some other countries such as France and Germany previously suggested the Oxford AZ vaccine was ineffective in older people, so many more younger people had this jab – which may have led to a higher incidence of this clotting problem. In actual fact the vaccine was shown to be very effective in older people so those countries were wrong in their earlier advice. So this advice may also change but the precautionary approach is sensible at this stage. We can expect more changes as time goes on and more experience and data is accumulated.

Should I have the Oxord AZ vaccine? Certainly if you are in the over 30 age groups and especially if you have other health conditions, the benefits of having this vaccine vastly outweigh any known risks. The advice may change but this is the current situation.

More about the risks from the BBC website