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AstraZeneca Covid-19 vaccine: safety and side effects

24 Mar 2021

Since some European countries paused use of the AstraZeneca Covid-19 vaccine, it’s now been deemed safe for administration. Dr Rhianna McClymont, Lead GP at Livi, answers some key questions

The UK vaccination programme has so far been very successful. As of the 21st March, over 27 million people have now received their first Covid-19 vaccine.

Recent concerns about the safety of the Oxford/AstraZeneca (AZ) vaccine caused some European countries to pause administration. But following investigation, it’s deemed safe to continue the roll out as, according to the World Health Organisation (WHO), the benefits outweigh the risks.

Here’s what you should know.

Is the AstraZeneca vaccine safe?

All of the Covid-19 vaccines – including the AstraZeneca vaccine – were thoroughly assessed for safety. Clinical trials involving over 20,000 people were carried out prior to the AZ vaccine being licensed, and no safety steps were skipped or ‘fast-tracked’ here.

It is true that the Covid-19 vaccines were developed more quickly than we’ve seen in the past. But this is thanks to immense financial investment, a significant number of scientists focused on the same goal, and large availability of clinical trial participants.

Even after they’re licensed, vaccines continue to be monitored closely for any adverse and rare side effects to make sure they remain safe for use.

What AstraZeneca side effects have been reported?

All medications or vaccines – including the common flu vaccine – have potential side effects. In the case of Covid-19 vaccines, side effects like a sore arm, temperature or aches and pains are not uncommon.

A small number of people suffered blood clots after having the AstraZeneca vaccine, which could be an extremely rare side effect.

Specifically, these few reports include cases of deep vein thrombosis (DVT), pulmonary embolism (PE), cerebral sinus vein thrombosis (CSVT) and bleeding related to low platelets.

What’s the risk of blood clot following the AstraZeneca vaccine?

So far, out of 17 million people vaccinated with the Oxford/AstraZeneca vaccine, there have been only:

  • 15 reported cases of deep vein thrombosis (DVT)
  • 22 cases of pulmonary embolism (PE)

In the UK specifically, out of 11 million people vaccinated there have also been:

  • 35 reports of low platelets and bleeding
  • 5 cases of a blood clot in the brain (CSVT)

What's the risk of a blood clot otherwise?

It’s important to remember that the background – or natural – risk of a blood clot occurring at some point in a person’s life is 1-2 in 1000 cases each year. Two thirds of these cases are caused by DVT and one third by PE.

This means statistically, it’s highly likely that the reports of clots are natural coincidence, rather than being caused by a vaccine.

What about blood clots in the brain?

The European Medicines Agency (EMA) is continuing to look into evidence that a CSVT, and a condition causing low platelet levels, may be associated with the vaccine. The EMA says, ‘A causal link with the vaccine is not proven, but is possible and deserves further analysis.’

A CSVT is an extremely rare type of clot which can occur naturally. In fact, the normal incidence of CSVT per year is 3 to 4 cases in every 1 million people. Currently in the UK, there have been 5 cases out of 11 million people vaccinated with AstraZeneca. The reports affect mainly women under the age of 55.

Anyone who’s been vaccinated and has a headache or unusual bruising that lasts more than 4 days should get medical advice – just as a precaution.

Are there risks of a blood clot from Covid-19?

It’s already well documented that a serious case of Covid-19 carries a high risk of blood clotting events. In someone admitted to hospital with Covid-19 there’s a 1 in 6 risk of developing a clot in the leg or lung, and a 1 in 12 risk of abnormal bleeding.

Because of this, a ‘risk vs benefit’ assessment is important when looking at vaccines – and this is what the regulators have done in the case of AstraZeneca and other Covid-19 vaccines.

What do the regulators say about AstraZeneca?

Having looked at all the evidence and following a rigorous scientific review, the UK’s regulator, the MHRA, confirmed on 18th March that the evidence does not suggest blood clots in the veins are caused by the AstraZeneca vaccine.

The European Medicines Agency (EMA) advises AstraZeneca is a “safe and effective vaccine” which protects people from risks of death and hospitalisation from Covid-19. This announcement has led to EU countries, like Italy, France and Germany, continuing administration.

Use of the AstraZeneca vaccine is also backed by WHO. ‘At this time, WHO considers that the benefits of the AstraZeneca vaccine outweigh its risks and recommends that vaccinations continue.’

Read advice from an infectious diseases specialist on what happens after you’re vaccinated for Covid-19.

This article has been written by Dr Rhianna McClymont, Lead GP at Livi, and reviewed by Harriet Bradley, Livi’s Medical Director.

Dr Rhianna McClymont
Lead GP at Livi
Last updated:

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