Extremely Rare Blood Clot FAQs

Joint Committee on Vaccination (JCVI) statement

An extremely rare adverse event of thrombosis (blood clots) and thrombocytopenia (low platelets – type of blood cell) have been noted after 1st vaccination with AstraZeneca. Click here for more information.

This condition is also known as “vaccine induced thrombocytopenic thrombosis” (VITT)

What is my risk of getting a clot (VITT) after the vaccine?

The data so far suggests that the risk of clot is an extremely rare adverse event associated with low platelets (a type of blood cell)  after vaccination with the Oxford/AstraZeneca vaccine. This is usually experienced between day 4-28 after vaccination.

How will I know if I might have a clot (VITT)?

Clots linked to the Oxford/AstraZeneca vaccine have been experienced between days 4-28 after vaccination. Possible signs you might have a blood clot include:

  1. a new, severe headache which is not helped by usual pain relief or is getting worse
  2. a headache that is worse when lying down or bending over
  3. a headache with blurred vision, nausea and vomiting, difficulty with speech, weakness, drowsiness or seizures
  4. new, unexplained bruising or bleeding
  5. shortness of breath
  6. chest pain
  7. leg swelling
  8. persistent abdominal pain

I have a family history of blood clot, does this put me at increased risk of a VITT?

Unless you have a personal history of one of the following listed conditions, you can proceed with the 2nd vaccination with Astra Zeneca

  • A history of cerebral venous sinus thrombosis -acquired or hereditary thrombophilia
  • Heparin-induced thrombocytopenia and thrombosis (HITT or HIT type 2)

I have had a previous clot – DVT (deep vein thrombosis) and/or PE (pulmonary embolus), is it safe for me to have the vaccine?

There is no evidence that patients with previous history of clots are more at risk of developing this rare effect after the vaccine.  The risk of clots from Covid-19 disease itself is far greater that the risk of this rare adverse effect from vaccination.

I am on the contraceptive pill. Can I have the vaccine?

The contraceptive pill is not known to increase the chance of this rare adverse effect with the covid-19 vaccination

Why have other countries stopped vaccinating with AstraZeneca, is it safe to have?

Every country has a medicines authority to make decisions for based on the information they have. The UK has the MHRA (Medicines and Healthcare product Regulatory Authority) and JCVI, (Joint Committee on Vaccination and Immunisation). They thoroughly assess all the data and weigh up the risk and benefit of the vaccination.

The decision in the UK is that the benefits of prompt vaccination with the Astra Zeneca Covid-19 vaccine far outweigh the risk of extremely rare adverse effects for individuals over 40 years old and those with underlying health conditions putting them at increased risk of Covid-19 disease.

The WHO (World Health Organisation) and the European Medicines Agency have also concluded that the balance of risk/benefit is very much in favour of vaccination.

Can I choose to have another vaccine that is not AstraZeneca for my second one?

All those who have received the 1st dose of Astra Zeneca should continue to be offered the 2nd dose of Astra Zeneca, irrespective of age, unless major clots were experienced with low platelets after the 1st dose.

Why have under 40 year olds been offered another vaccine?

There appears to be an increasing incidence of these rare adverse effects in the younger age groups. The risks of serious adverse effects from Covid-19 disease increases significantly with age. With the covid-19 case numbers much lower currently, the risk of severe illness/death from covid in these younger age groups is very low.

Therefore, as a precaution, under 40yr olds without underlying health conditions can be offered another vaccine (if available) for their first Covid-19 vaccine but can still make an informed decision to receive the Astra Zeneca vaccine to receive earlier protection.

For the second vaccine, individuals aged 18-39 years can proceed with having Astra Zeneca if no serious adverse effects experienced after their first vaccination with Astra Zeneca.


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