MHRA updates AstraZeneca Covid-19 vaccine guidance following blood clotting reports

People with a higher risk of blood clots should only be offered the Oxford/AstraZeneca Covid-19 vaccine if the benefits of protection from Covid-19 outweigh any potential risks.

The announcement comes after the Medicines and Healthcare products Regulatory Agency (MHRA) updated its information on the possible risk of blood clots occurring following the administration of the Oxford/AstraZeneca Covid-19 vaccine.

Whilst the MHRA says that blood clots following vaccination are very rare and unlikely to occur, there is now evidence of a link between the Oxford/AstraZeneca Covid-19 and specific blood clots. In particular, the MHRA investigated the link between cerebral venous sinus thrombosis (CVST) occurring together with low levels of platelets (thrombocytopenia) following vaccination with the Oxford/AstraZeneca vaccine.

At this point, the MHRA is not recommending age restrictions for the Oxford/AstraZeneca vaccine but the government’s Joint Committee on Vaccination and Immunisation (JCVI) has said that adults under 30 should be offered an alternative vaccine if available.

This is due to data suggesting that there is a higher incidence of risk related to the vaccine in people under 30. The data examined the 20.2 million doses of the Oxford/AstraZeneca Covid-19 vaccine which had been administered by 31 March 2021 in the UK. Up until this date, the MHRA received 79 reports of blood clotting cases alongside low levels of platelets following the use of the Oxford/AstraZeneca Covid-19 vaccine. Of these, 44 of the 79 cases of CVST with thrombocytopenia whilst the remainder were of thrombosis in other major veins with thrombocytopenia. Sadly, 19 people have died with 11 of those being under the age of 50, three of whom were under 30.

From these data, the approximate risk of these blood clots occurring is four people in a million who receive the vaccine.

The MHRA has confirmed that the evidence does not suggest that the Oxford/AstraZeneca Covid-19 vaccine causes venous thromboembolism without a low platelet count. The MHRA also says that it is important to highlight that this type of blood clot can occur in people naturally.

As a precautionary measure, the MHRA is calling on people who have symptoms four days or more after vaccination to seek medical attention. Symptoms include:

• a new onset of severe or persistent headache, blurred vision, confusion or seizures.
• develop shortness of breath, chest pain, leg swelling or persistent abdominal pain.
• unusual skin bruising or pinpoint round spots beyond the injection site.

Dr June Raine, MHRA chief executive, said: “Over 37 million doses of vaccines against Covid-19 have now been administered in the UK, saving thousands of lives through the biggest vaccination programme that has ever taken place in the UK.

No effective medicine or vaccine is without risk. We continually monitor safety during widespread use of any vaccine. This is to ensure vaccines are performing as expected, to identify any new side effects that may arise, and to ensure the benefits continue to outweigh the risks.

The public’s safety is always at the forefront of our minds and we take every report of a suspected side effect very seriously indeed. We thoroughly analyse each and every report as we receive it and although the number of reports of CVST and other thromboembolic events has increased over the last week, so has the overall number of vaccinations administered, therefore these blood clots remain extremely rare and unlikely to occur.

We ask anyone who suspects they have experienced a side effect linked with their Covid-19 vaccine to report it to the Coronavirus Yellow Card website. It is still vitally important that people come forward for their vaccination when invited to do so.”

In response to the updated guidance, AstraZeneca released a statement saying: “Updates to the UK and EU labels for the vaccine have been requested by the regulators. Neither agency identified any risk factors, such as age or gender, or a definite cause for these extremely rare events. However, they came to the view that these events have a possible link to the vaccine and requested they be listed as an extremely rare potential side effect.

Overall, both of these reviews reaffirmed the vaccine offers a high-level of protection against all severities of Covid-19 and that these benefits continue to far outweigh the risks.

AstraZeneca has been actively collaborating with the regulators to implement these changes to the product information and is already working to understand the individual cases, epidemiology and possible mechanisms that could explain these extremely rare events.”

The World Health Organisation (WHO) has said that a causal relationship between the vaccine and the occurrence of blood clots with low platelets is considered plausible but is not confirmed. More specialised studies are needed to fully understand the potential risk factors, WHO says.