Recently there have been reports of a very rare condition involving blood clots and unusual bleeding after vaccination. This is being carefully reviewed but the risk factors for this condition are not yet clear.
Although this condition remains extremely rare there appears to be a higher risk in people shortly after the first dose of the AstraZeneca (AZ) vaccine. Around 4 people develop this condition for every million doses of AZ vaccine doses given.
This is seen slightly more often in younger people and tends to occur between 4 days and 2 weeks following vaccination.
This condition can also occur naturally, and clotting problems are a common complication of COVID-19 infection. An increased risk has not yet been seen after other COVID-19 vaccines but is being carefully monitored.
It is important to note in all groups, the benefit of receiving the vaccine and being protected against the serious consequences of Covid outweigh any risk of blood clotting.
Below there are details of advice for people in different groups.
You’re over 50 or have underlying medical conditions:
The advice says you should still receive any of the available vaccines. If your first dose was AZ, and you had no serious side effects, you should have the second AZ dose too. The second vaccine will give you higher and longer-lasting protection.
You’re a healthy person between 30 and 50:
As above, you should still receive any available vaccine. If you have had your first vaccine, you should complete your course with the same vaccine.
You’re a healthy person aged 18 to 29:
The safety of the AZ vaccine in younger people continues to be monitored. It’s preferable for people in this group to have another vaccine than AZ. Choosing alternative means you may need to wait longer to be protected. You should carefully consider the risk to both you and your family and friends of COVID-19 before making a decision.
What is blood clotting?
Blood clots can be very serious and need to be treated quickly. They are also rare in young and healthy people.
Common symptoms include throbbing or cramping pain in the leg or arm, redness, warmth and swelling, or sudden breathlessness or sharp chest pains. You can read more on blood clots at the NHS website.
Blood clots occur naturally at a rate of between 5-16 in every 1,000,000 people.
It’s estimated that around 4 in every one million people who have had a first dose of the AZ vaccine have developed blood clots. The full factsheet from Public Health England can be found at this link.