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Guidance on blood clots with Oxford/AstraZeneca vaccine in under 30s

Data suggests there is a higher risk of extremely rare blood clots following the first dose of the Oxford/AstraZeneca vaccine

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This article was correct at time of publishing (April 8) and supersedes C+D’s article, published on April 1, on the Safety of the Oxford/AstraZeneca COVID-19 vaccine. For further news and updates please visit C+D’s COVID-19 hub.

The Medicines Healthcare and Regulatory Agency (MHRA) and the Joint Committee on Vaccination and Immunisation (JCVI) have confirmed that the benefits of the Oxford/AstraZeneca COVID-19 vaccine continue to outweigh the risks of developing COVID-19, following a meeting on April 7.

The MHRA has concluded a possible link between the Oxford/AstraZeneca vaccine and an extremely rare, unlikely link to blood clots occurring, however more scientific evidence is required for a firm conclusion. It is estimated that the risk of blood clots in those receiving the Oxford/AstraZeneca vaccine is four in one million and a slightly higher incidence has been reported in younger adults.

Incidence of adverse effects

As of March 31, it was estimated that around 20.2 million people in the UK had received the Oxford/AstraZeneca vaccine. The MHRA has received 79 UK reports of blood clotting (thrombosis) cases alongside low levels of platelets (thrombocytopenia) following the first dose of the Oxford/AstraZeneca vaccine. This risk is higher than that calculated from previous reports, up to and including March 24, however the risk of these blood clots occurring is still extremely rare. These reports have been analysed by the government’s independent advisory body, the Commission on Human Medicines and its COVID-19 Vaccines Benefit Risk Expert Working Group, which includes lay representatives and advice from leading hematologists.

There are currently no reports of thrombosis or thrombocytopenia events, which are extremely rare, following the second dose of the Oxford/AstraZeneca vaccine.

What does the MHRA advise?

The MHRA has advised that those at higher risk of blood clots should be considered for the Oxford/AstraZeneca vaccine only if benefits from the protection from COVID-19 infection outweighs potential risks of vaccination. This includes patients with a history of cerebral venous sinus thrombosis, acquired or hereditary thrombophilia, heparin-induced thrombocytopenia or antiphospholipid syndrome. As pregnancy can increase the risk of thrombosis, these risks vs benefits should also be discussed with pregnant women.

Patients who experience symptoms of cerebral or other major blood clots occurring with low levels of platelets after their first vaccine dose of Oxford/AstraZeneca should not be offered the second dose.

Patients who did not have any symptoms of cerebral or other major blood clots occurring with low levels of platelets after their first dose should receive the second dose when invited, unless advised otherwise by a healthcare professional.

The MHRA has confirmed that the evidence to date does not suggest that the Oxford/AstraZeneca vaccine causes venous thromboembolism without a low platelet count. Patients should be advised that this type of blood clot, together with lowered platelets, can in rare cases occur naturally in unvaccinated people as well as in people with COVID-19. The MHRA is currently not recommending age restrictions for the Oxford/AstraZeneca vaccine.

What does the JCVI recommend?

The JCVI advises that the benefits of prompt vaccination with the Oxford/AstraZeneca COVID-19 vaccine far outweighs the risk of adverse events for individuals 30 years of age and over and those who have underlying health conditions that put them at higher risk of severe COVID-19 disease.

The JCVI currently advises that it is preferable for adults aged under 30 years without underlying health conditions that put them at higher risk of severe COVID-19 disease, to be offered an alternative COVID-19 vaccine, if available. Alternative vaccines currently approved for use in the UK include the Pfizer/BioNTech and the Moderna vaccine.

The JCVI has also advised that these patients may also make an informed choice to receive the Oxford/AstraZeneca vaccine to receive earlier protection.

Those under 30 years who have been prioritised to receive a vaccine in phase 1 due to an increased risk of exposure and/or to reduce the risk of passing the infection on to vulnerable individuals should be offered an alternative vaccine if they have yet to receive their first Oxford/AstraZeneca vaccine. The JCVI is finalising its advice on phase 2 of the programme, particularly for healthy people under 30 years.

Those who have received a first dose of the Oxford/AstraZeneca vaccine should continue to be offered a second dose of Oxford/AstraZeneca COVID-19 vaccine irrespective of age because the second dose is important for longer lasting protection against COVID-19.

What advice can the pharmacy team give?

The MHRA has issued updated guidance for healthcare professionals on how to minimise risks, as well as further advice on symptoms for vaccine recipients to look out for four or more days post-vaccination.

All individuals offered a COVID-19 vaccine should be fully informed about the benefits and risks of vaccination, and pharmacy teams should emphasise that the benefit of receiving the vaccine currently outweighs the risk of COVID-19 and potential vaccine side effects.

Patients should be advised to be alert for possible cases of extremely rare thrombosis/thrombocytopenia. Patients should be advised to seek immediate medical attention if they develop any of the following symptoms after vaccination:

  • shortness of breath, chest or persistent abdominal pain, leg swelling
  • blurred vision, confusion or seizures
  • unexplained pin-prick rash or bruising beyond the injection site.

Patients who experience symptoms of new onset severe or persistent headache that does not respond to simple painkillers starting four days or more after vaccination should be advised to speak to their doctor.

As with all medicines, close safety monitoring will continue, with additional studies being carried out to provide more laboratory data, as well as real-world evidence. You can find further information on side-effects associated with COVID-19 vaccines by reading the C+D article: What adverse reactions can occur with the COVID-19 vaccines?

Patients can be signposted to and the patient information leaflet for more information.


Both the MHRA and JCVI have made clear the benefit of receiving the Oxford/AstraZeneca vaccine outweighs the risk. NHS England has released ‘next-steps’ guidance for vaccination centres for continued roll out of this life-saving programme.


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