Serious thromboembolic events with concurrent thrombocytopenia (a blood clot), sometimes accompanied by bleeding, have occurred very rarely following vaccination with the Oxford-AstraZeneca COVID-19 vaccine during post-authorisation use. This includes life-threatening and fatal cases presenting as venous thrombosis, including unusual sites such as cerebral venous sinus thrombosis, splanchnic vein thrombosis, as well as arterial thrombosis, combined with thrombocytopenia that can rapidly progress. Multifocal venous and arterial thromboses have been reported in serious cases. The majority of the events occurred within the first 14 days following vaccination but have also been reported after this period.

Healthcare professionals should be alert to the signs and symptoms of thromboembolism and/or thrombocytopenia. Vaccinated individuals should be instructed to seek immediate medical attention if they develop new symptoms such as shortness of breath, chest pain, leg swelling, persistent abdominal pain, any neurological symptoms or signs (such as blurred vision, confusion or seizures) or unusual skin bruising and/or petechiae after vaccination. Vaccinated individuals should also seek immediate medical attention if they develop new onset or worsening persistent headaches which do not respond to simple painkillers four or more days after vaccination.

The MHRA advise that the benefits of vaccination continue to outweigh any risks. However, they also advised that careful consideration be given to people who are at higher risk of specific types of blood clots because of their medical condition, particularly in relation to the AstraZeneca jag. Please see the "further information" section for a information slides regarding the AstraZeneca vaccine.

In the UK, people under-30 and those without an underlying health condition will be offered alternative to Oxford-AstraZeneca jag.

Commenting, Professor Angela Thomas, acting president of the Royal College of Physicians of Edinburgh said:

The College notes that the risk of developing a blood clot after receiving the AstraZeneca jag is very small. This scenario illustrates the importance of collecting and analysing safety data in real time, as the UK begins to rollout the vaccines to groups where the risks of serious illness from COVID-19 infection are less.

The current vaccine rollout programme is unprecedented. It is unlikely that there has ever been a vaccine or drug roll out on such a large scale, over such a short space of time, and with such scrutiny by the public and media.

While the news of blood clots may appear concerning, they are incredibly rare. The occurrence of blood clots in those vaccinated is magnified by the scale and speed of the vaccine programme. Normally, it would take several years to uncover the extent of side effects relating to a vaccine or drug, especially if they are very rare.

It is important to identify potential side effects of any new vaccine as soon as possible, and to alert both the medical profession and the public so that steps can be taken to reduce risk. The large number of people vaccinated over a short space of time has allowed such rapid identification of the possible link of the AstraZeneca jag to blood clots.

The College would advise people to follow the public health guidance on the AstraZeneca jag, which is to receive it unless they are under 30 years of age and they don’t have an underlying health concern – in which case they will be offered an alternative vaccine.