Dr Amir Khan has shared three blood clot symptoms recipients of the AstraZeneca vaccine jab should know about.
The warning comes as investigations continue into potential links between the AstraZeneca jab and blood clots.
Dr Khan appeared on Wednesday morning’s instalment of Good Morning Britain alongside hosts Adil Ray and Ranvir Singh.
Dr Amir said: "It is common to get minimal side effects after having the vaccine such as headaches, a temperature, fevers, chills, but if your headache persists beyond four days after having the vaccine, then you should seek medical help.
"Other symptoms include blurred vision and nausea, and then as time develops, if you do not get treatment, that can progress then to seizures and such.
"But in particular headaches, blurred vision, nausea, particularly after four days, is when you should seek medical help."
Despite the concerns, Professor Adam Finn, from the University of Bristol and a member of the JCVI, said it was vital to keep vaccines going as society opens up, in order to help stave off rising infection rates.
It comes as the Medicines and Healthcare products Regulatory Agency (MHRA) and the European Medicines Agency (EMA) are expected to give updates on their investigations into whether the Oxford/AstraZeneca vaccine is directly causing rare brain blood clots.
Some European countries have restricted the vaccine use in younger people following reports of low platelet counts and cerebral venous sinus thrombosis (CVST), a specific type of clot that prevents blood from draining from the brain.
Asked if different vaccines could end up being used for certain groups as more vaccine types come on stream, Prof Finn told BBC Breakfast: “That’s certainly possible. We are seeing another vaccine coming in (Moderna), and further vaccines are approaching licensure, and I know that the UK has made contracts for quite a wide range of different vaccines.
“As time goes forward, we will have much more flexibility about who can be offered what.
“On the other hand, we do need to keep the programme going if the plan to open things up and allow things to get back to normal is to proceed without another wave of the pandemic coming through.
“So it’s quite a tricky balancing act here, getting the balance right, getting vaccines coming through… getting the risk-benefit right for people coming forward.”
Prof Finn told BBC Radio 4’s Today programme the reports of clots were being investigated “very seriously” and “very thoroughly”.
He said: “What stands out about them is that we see thrombosis, including thrombosis in the cerebral veins, all the time, but we don’t normally see them in association with a low platelet count – which is a small blood cell which is involved in blood clotting – and so that makes them stand out and makes us think that this is something a little bit different and out of the norm.”
Earlier this week it was reported that the MRHA had considered telling those under the age of 30 to avoid taking the AstraZeneca vaccine.
Following further research, the organisation said the benefits of the vaccine far outweighed any risk and urged the public to continue taking the vaccine.
Speaking on GMB Dr Khan added: "That is right. It is all about the risk benefit.
"But even still, even in the younger category, the risk of these clots if you look at the data in general is about 1 in 100,000 people who get the AstraZeneca MAY go on to get the clot.
"If you look at the data in Covid in under-40s, you have a 1 in 1,000 chance of dying if you are under-40.
"The benefits still outweigh the risk in all age groups and we have to discover whether there is a causal link between the vaccine and clots.
"In the meantime, the MHRA is telling people to keep on taking up offers of a vaccine jab."
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