What did regulators say at the time?

A review by EMA safety committee, at the time of the discovery of the clots in June 2021, concluded that “unusual blood clots with low blood platelets should be listed as very rare side effects” of the AstraZeneca vaccine.

Emer Cooke, executive director of the EMA, said: “The risk of mortality from Covid is much greater than risk of mortality from these side effects.”

The MHRA always said that there were still huge benefits of the vaccine in preventing Covid-19 and serious disease but added that due to a very small number of blood clots in younger people, those under the age of 40 were to be offered Pfizer or Moderna jabs instead.

Dr June Raine, MHRA chief executive, added: “Anyone who has symptoms four days after vaccination or more should seek prompt medical advice – a new onset of a severe or persistent headache or blurred vision, shortness of breath, chest pain, leg swelling, persistent abdominal pain or indeed unusual skin bruising or pin-point spots beyond the injection site.”

How did other countries react?

Germany, the Netherlands, Sweden and Canada all restricted the use of the AstraZeneca vaccine in younger people. Italy and Spain stopped the use of the  jab in the under-60s.

Denmark announced on Apr 14 2021 that it would stop administering Oxford/AstraZeneca’s Covid-19 vaccine entirely following its link to very rare cases of blood clots, a decision based on the low levels of Covid-19 in the country and caution over the rare side-effect. 

The decision, which at least for now removes the shot from Denmark’s vaccination scheme, could delay the country’s vaccine rollout by up to four weeks, based on previous statements by health bodies.

Also in Apr 2021, France said under 55s who have had a first AstraZeneca dose should take a different vaccine for the second. Olivier Véran, the country’s health minister, said the new advice will be that the Moderna and Pfizer vaccines should be used for their second dose.

Spain began studying the effects of mixing different coronavirus vaccines, government researchers said on Apr 19 2021, responding to shifting guidelines on the safety of the AstraZeneca’s shot.

Also, Australia doubled its order of the Pfizer Covid-19 vaccine, as the country began its race to overhaul its inoculation plan over concerns about the risks of blood clots with the AstraZeneca vaccine.

Many of the decisions to restrict the use of the jab also have to be seen in the context of a country having access to other jabs, and low rates of Covid. 

What was AstraZeneca’s response?

In March 2021, AstraZeneca said it was analysing its database to understand “whether these very rare cases of blood clots associated with thrombocytopenia (low blood platelet count) occur any more commonly than would be expected naturally in a population of millions of people”.

Meanwhile on Apr 6, a trial of the Oxford/AstraZeneca vaccine on children was paused, but the scientists involved said there were no safety concerns with the trial itself and they were waiting for further information from the MHRA.

In response to these concerns, an Oxford University study examined the incidence of blood clotting on the brain in coronavirus patients and AstraZeneca recipients, finding that the occurrence of brain clots from coronavirus was eight times greater than the risk presented by the AstraZeneca jab.

Sir John Bell, Oxford University’s Professor of Medicine, stated that he expected all vaccines to have “some background level of clotting issues”. Prof Sir Bell went on to say that the data on this issue was still being collected for further study.

What about the Johnson and Johnson vaccine and blood clots?

Regulators in the United States paused the roll out of the Johnson and Johnson vaccine after six people suffered blood clots two weeks after receiving the jab – one person died. Regulators say the decision is based on an “abundance of caution”, and have since resumed use of the jab after a safety review. 

The decision is already being felt more widely: the company delayed shipments of the vaccine to Europe. And South Africa, which decided to stop using the AstraZeneca vaccine because of lack of efficacy against a new variant, has also put its campaign on pause. 

On Apr 20, the European Medicines Agency (EMA) said there was a possible link between Johnson & Johnson’s Covid-19 vaccine and rare blood clots but said the benefits of the J&J vaccine far outweighed the risks and that further investigations would continue. 

The single-dose Johnson & Johnson vaccine was approved for use in the UK as of May 28 2021. The government has ordered 20 million doses, which will be used to target “hard-to-reach” groups in the vaccine rollout, such as those who may be reluctant to come forward for two jabs. Additionally, the Janssen vaccine will potentially be used as part of a booster programme later in the year.

What are the side effects of the Oxford/AstraZeneca vaccine?

The AstraZeneca vaccine lists the following side-effects that can occur after the jab: tenderness, pain, warmth, itching or bruising where the injection is given, generally feeling unwell, feeling tired, chills or feeling feverish, headache, feeling sick (nausea), joint pain or muscle ache.

Ian Douglas, professor of pharmacoepidemiology at London School of Hygiene and Tropical Medicine, explains that these side-effects are “pretty common” and occur in more than one in 10 people who are given the vaccine.

When should I see a doctor?

While some people will experience side-effects from the jab, experts have said that certain symptoms may be a sign of a more serious condition which needs immediate medical attention.

Prof Beverley Hunt, medical director at the charity Thrombosis UK, said thrombosis in the head can present as an extremely bad headache.

“We’ve seen patients who have been presenting with thrombosis in the head or abdomen from about day four after the vaccine,” she said.

“I think it’s very important to tell people that lots of people get side effects from the AstraZeneca vaccine and they usually settle down by day four or five.

“What we’ve seen is people presenting with the worst headache they have ever had on day four and they have proved to have thrombosis in the large vein of the head.”

What factors increase the risk of blood clots?

Blood clots are rare in young, healthy people. Below is a list of factors that can make them more common, although it is not clear if these factors are involved in the post-vaccination events, which are a specific kind of clot occurring alongside low platelets. In fact, haematologists have said there is currently no evidence these groups are more at risk of this side-effect. 

Generally, you are more likely to experience a blood clot if you: 

• Are staying in or recently left hospital – especially if you cannot move around much (like after an operation)
• Are overweight
• Smoke
• Are using combined hormonal contraception such as the combined pill, contraceptive patch or vaginal ring
• Have had a blood clot before
• Are pregnant or have just had a baby
• Have an inflammatory condition such as Crohn’s disease or rheumatoid arthritis

What other vaccines are available?

The UK is currently administering all four vaccines: Pfizer/BioNTech, Moderna, Janssen and Oxford/AstraZeneca (for those over the age of 40 and for anyone who might experience side effects from the other three jabs).

The Valneva Covid-19 vaccine was set to be manufactured in the UK as preliminary test results showed it produces a “strong immune response”, paving the way for a phase three clinical trial.

However, the UK dropped its deal to receive approximately 100 million doses in September 2021, after the UK Health Secretary Sajid Javid told the House of Commons that the vaccine would not have passed UK regulations.