AstraZeneca (AZ) Vaccine and blood clotting

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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 are not yet clear

Although this is extremely rare, there appears to be a higher risk in people shortly after the first dose of the AstraZeneca (AZ) vaccine.

Around four people develop this condition for every million doses of the AZ vaccine given, this is seen slightly more in younger people and tends to occur between four days and two weeks following the first dose vaccination.

This condition can also occur naturally, and clotting problems are a common complication of the COVID-19 infection, an increased risk has not yet been seen after other COVID-19 vaccines, but this is being carefully monitored.


New guidance from June 2021

Guidance about the eligibility of adults under the age of 40:

  • Healthy adults under the age of 40 will receive either the Pfizer or the Moderna vaccine and are now not eligible to receive AstraZeneca.

  • Healthy adults under the age of 40 who have already received their first dose of AstraZeneca are still eligible to receive their second dose of AstraZeneca.

  • Individuals under the age of 40 who already have a first dose of AstraZeneca booked, will have their appointments cancelled and will be invited and given advice on how to re-book a Pfizer or Moderna vaccine via the National Booking System.


Anyone under 40 attending vaccination clinics for a first dose AZ vaccine will be advised they need an alternative vaccine and must re-book their first and second doses. Appointments can be booked via the National Booking System.

Some clinics may be able to offer an alternative vaccine at the time; these patients should be advised to book their second dose via the national boking system after their first dose.

This guidance is in line with the JCVI guidance on vaccinating people under the age of 40, and is also highlighted in Chapter 14a of the Green Book (page 15).

Healthy adults aged 18-39 years

Evidence suggests that the risk of serious COVID-19 disease is strongly related to age, and the risk of COVID-19 mortality, hospitalisation and ICU admission is lower in younger adults. Based on the current epidemiological situation, and taking into account projected vaccine supply, JCVI are advising a preference for a vaccine other than AstraZeneca to be offered to healthy people under 40 years of age, including health and social care workers, unpaid carers and household contacts of immunosuppressed individuals.

This advice may change if there is a change in the epidemiology or an interruption in the supply of the alternative vaccines. Within this age group, those who are older (over 30 years of age), male, from certain minority ethnic backgrounds, in certain occupations at high risk of exposure, and those who are obese, remain at high risk of COVID-19. In the absence of a suitable alternative these individuals should still be offered the AstraZeneca vaccine, and may choose to receive the vaccine, provided they have been informed and understand the relative risks and benefits. They should be given the latest version of the COVID-19 vaccination and blood clotting leaflet ( ).

Those who have already received a dose of AstraZeneca vaccine should complete with the same vaccine (see contraindications and precautions).

As a precautionary measure, anyone who has the following symptoms from around 4 days to 4 weeks after vaccination is advised to seek prompt medical advice:

a severe headache that is not relieved with painkillers or is getting worse

a headache that feels worse when you lie down or bend over

a headache that is unusual for you and occurs with blurred vision, feeling or being sick, problems speaking, weakness, drowsiness or seizures

a rash that looks like small bruises or bleeding under the skin

shortness of breath, chest pain, leg swelling or persistent abdominal pain.


Worried about your second AZ vaccine? Find out more here