Scientists are looking into whether cases of a rare type of blood clot are connected to the Oxford-AstraZeneca coronavirus vaccine.
The UK medicines regulator has said the benefits of the jab continue to outweigh any risks, but under-30s will now be offered an alternative vaccine.
It comes after a review found that 79 people had suffered rare blood clots after vaccination by the end of March - 19 of whom had died.
However, the regulator said this was not proof the jab had caused the clots, but that the link was 'getting firmer'.
There are still 700,000 Scots under 30 who have still to receive their vaccines and will now be given either the Pfizer or Moderna jabs.
Here's everything we know so far about the rare blood clots:
What are the rare blood clots?
Known as CVSTs, the clots are found in a large vein in the brain.
It's not yet known why the vaccine could cause them, but there are a few things scientists are exploring.
In the cases under investigation, the patients were all found to have low numbers of platelets - blood cells that normally help repair bleeding in the body, the BBC reports.
A certain anti-body were also found in the patients' blood, causing the platelets to group together and form a clot.
How to tell if you have a blood clot
Symptoms like these are most likely within 'the first few days' of having the vaccination according to National Clinical Director Jason Leitch.
But he said: “If you have a serious blood clot you will know and you will know to seek medical care immediately. You are more likely to have a heart attack generally in life.”
These are the symptoms:
- A severe, persistent headache
- Blurred vision
- Shortness of breath
- Chest pain
- Leg swelling
- Persistent stomach/abdominal pain
- Unusual bruising or red/purple pinpoint spots beyond the injection site where the vaccine is given
- Neurological symptoms such as weakness in the legs or seizures
How rare are the clots?
More than 20 million doses of the AstraZeneca vaccine have been given in the UK.
Out of these vaccines, 79 cases of blood clots have been identified and 19 people have died.
It's estimated to be one in 250,000 people, which means it is classed as rare.
The EU's medicines regulator says unusual blood clots should be listed as a possible very rare side effect of the AstraZeneca jab, but that the benefits outweigh the risk.
The World Health Organization said the link between the vaccine and blood clots was "plausible" but not confirmed, adding that the clotting incidents were "very rare".
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