AstraZeneca Covid vaccine: safety and side effects

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Is the AstraZeneca vaccine still being used in the UK?
What side effects can the AstraZeneca vaccine have?
Can the AstraZeneca vaccine cause blood clots?
Why might these rare blood clots happen?

Is the AstraZeneca vaccine still being used in the UK?

No, the UK government stopped using the AstraZeneca Covid-19 vaccine in winter 2021. In May 2024, AstraZeneca withdrew the vaccine, now called Vaxzevria, from sale in other countries.

The AstraZeneca vaccine played an important role in the UK's life-saving vaccine programme during the early stages of the pandemic, but evidence shows that mRNA vaccines, Pfizer and Moderna, are more effective at boosting protection from Covid-19. These vaccines have also been updated to tackle more recent Covid-19 variants, and these are the vaccines now used in the UK's seasonal booster programmes.

What side effects can the AstraZeneca vaccine have?

While the Oxford/AstraZeneca vaccine is no longer being offered in the UK, the Medicines and Healthcare products Regulatory Agency (MHRA) still monitors potential side effects from this vaccine.

Most side effects that have been reported for the Oxford/AstraZeneca vaccine are mild and short-term. The most common side effects are: discomfort at the injection site, or feeling generally unwell, tired, or feverish, or a headache, feeling sick or having joint or muscle pain.

Visit the NHS for the full list of possible side effects for the AstraZeneca vaccine.

Can the AstraZeneca vaccine cause blood clots?

Blood clots in combination with low platelet levels (thrombocytopenia) are listed as a very rare side effect of the AstraZeneca vaccine. Most cases were observed in the first 3-4 weeks after vaccination.

In April 2021, the Medicines and Healthcare products Regulatory Agency (MHRA) confirmed a possible link between the AstraZeneca Covid-19 vaccine and these rare blood clots, but emphasised that the benefits of the vaccine continued to outweigh the risks for the vast majority of people.

The cases of blood clots that the MHRA reviewed were accompanied by abnormally low levels of platelets in the blood. Platelets are involved in blood clotting, and these abnormally low levels can be a sign that your body’s normal clotting mechanisms are not working properly. Some of the blood clots were an unusual type of blood clot in blood vessels that drain blood from the brain called a cerebral venous sinus thrombosis (CVST).

Visit the MHRA Yellow Card report for the latest data on the reported side effects of Covid-19 vaccines.

Why might these rare blood clots happen?

Research from Cardiff University and Arizona State University, published in December 2021, found a possible explanation of the link between the AstraZeneca vaccine and rare blood clots. They discovered that the adenovirus in the vaccine (which is used to deliver genetic instructions to the cells) can bind with a protein found in the blood, called platelet factor 4. They think that in extremely rare cases, this may trigger a chain reaction in the immune system, which could result in blood clots developing.

More research still needs to be done in this area. The study authors hope that scientists will be able to build on these findings to reduce the risk of these extremely rare side effects, as well as informing the development of future vaccines.