Astrazeneca Covid vaccine Q&A: What we know about blood clots, side effects and risks

Regulators around the world have now concluded that very rare cases of a particular type of blood clot may be linked to the AstraZeneca/Oxford University vaccine.

However, the risk of the rare brain clot from the vaccine is eight times less than the risk of a clot caused by Covid-19, according to an Oxford University study.

Regulators, including the Medicines and Healthcare products Regulatory Agency (MHRA) in the UK and the European Medicines Agency, say the overall benefits of the vaccine outweigh the risks for all age groups.

However, for younger people, and particularly when Covid-19 transmission is low, the balance is more complex, as the charts below show.

That's why the Joint Committee for Vaccination and Immunisation (JCVI) says under-40s in the UK should get a different jab where possible, and European countries have set different age limits for the jab. The guidance follows the reports of post-vaccination cases of cerebral venous sinus thombosis (CVST) and some other clots, alongside low platelets, or thrombocytopenia.

The UK is now using the AstraZeneca vaccine, the Pfizer/BioNTech jab, and the newly available Moderna vaccine.

Prime Minister Boris Johnson has said people should follow the regulator's advice and keep getting their jabs.

Read on to find out the latest about the Oxford/AstraZeneca vaccine, and to have your questions answered by our expert, The Telegraph's Global Health Security Editor Paul Nuki, below.

What do we know about any link between the AstraZeneca vaccine and blood clots?

The number of serious blood clots reported after vaccination with the AstraZeneca jab continues to increase, but the Government's regulatory agency has said the benefits still outweigh the risks. The rate of increase has slowed after a jump when the link was first discovered.

Cases are now at 262, as of the weekly report up to May 5, and 51 deaths, according to the Yellow Card system which allows people to report vaccine side-effects.

The chance of having a clot has gone from one in 250,000 to one in 91,743, remaining extremely rare.

The rare blood clot events occurred in 149 women and 112 men, aged between 18 and 93, with a case fatality rate of 20 per cent, with 51 deaths.

"On the basis of this ongoing review, the advice remains that the benefits of the vaccine outweigh the risks in the majority of people," the MHRA has said. The European regulator, the European Medicines Agency, has come to the same conclusion. As discussed below, for younger people - particularly when Covid rates are low - the equation is slightly different.

What have the regulators said?

A review by EMA safety committee 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 said 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 will 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 have other countries reacted?

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

Denmark announced on Apr 14 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.

France has 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 will study the effects of mixing different coronavirus vaccines, government researchers said on Apr 19, responding to shifting guidelines on the safety of the AstraZeneca's shot.

Also, Australia has doubled its order of the Pfizer Covid-19 vaccine, as the country races 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 has AstraZeneca said?

In March of this year, 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, has stated that he expects 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 April 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.

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 using two vaccines, Pfizer/BioNTech and Oxford/AstraZeneca, while a third coronavirus vaccine, the Moderna jab, began its rollout in Wales on Apr 7.

Meanwhile, preliminary results announced on Apr 6 from the trials of the Valneva Covid-19 vaccine, which is set to be manufactured in the UK, have shown it produces a "strong immune response", paving the way for a phase three clinical trial.

The UK has an in-principle agreement for 60 million doses of the Valneva jab, with an option to acquire a further 130 million doses from 2022-2025.

The country has also ordered 30 million doses of a coronavirus vaccine developed by Johnson & Johnson, which has been shown to be 66 per cent effective in preventing coronavirus infection.

Both the Valneva and Johnson & Johnson jabs will need regulatory approval for use in the UK, once data from later-stage trials become available.

Readers' questions

We asked Telegraph readers for their questions on the vaccines that have been rolled out in the UK. Our expert, The Telegraph's Global Health Security Editor Paul Nuki, answered them on Thursday April 8. Above, we have updated the article based on emerging information. Below, you can read his answers from that date.

Read on for a selection of the best questions from the Q&A.

What are the blood clot risks of the different vaccines currently used in the UK?

Q: What are the blood clot risks of the used vaccines apart from the AstraZeneca vaccine? How do they compare?

A: The other vaccines have not been associated with a raised incidence of clotting. With AZ there does seem to be a raised risk but the problem remains extremely rare.

The MHRA has said up to March 31, it had received "two reports of blood clots (thromboembolism) reported with thrombocytopenia for the Pfizer/BioNTech vaccine".

By this date, approximately 11 million first doses and 3.5 million second doses of the vaccine had been given, the MHRA said.

There is no data on the Moderna vaccine as it is not yet being used widely in the UK.

I've had one dose of AstraZeneca, but I'm under 30, what vaccine will I get for my second dose?

Q: If the AstraZeneca vaccine is banned in an age group what happens for my second dose if l had AstraZeneca for my first?

A: The AZ vaccine is not being banned in any age group. It is just that those under 30 are being offered a choice if an alternative is available. If you have had one dose of the AZ jab the very clear advice is that you should have your second. Any risk is tiny and the upside enormous, especially if we get another surge in infections later in the year –which is likely.

Is there evidence to suggest that we should have different vaccines for different doses?

Q: What evidence is available showing one jab of AstraZeneca vaccine and one jab of Pfizer vaccine provides better efficacy? Is it possible to get this treatment here in England?

A: I’m not aware of there being any evidence yet that mixing jabs has any additional benefit and there may be risks. It’s possible but we will only find out once proper trials have been done. If you search online you may be able to enter one.

Why should I risk getting a vaccine if I have already had Covid?

Q: Having had Covid (no symptoms, but loss of smell and taste), I fail to see why people not at risk, such as myself, are required to take the additional risk of vaccination. Why not stop after all the vulnerable are vaccinated?

A: The natural immunity you got when you first had Covid may not last long, leaving you exposed in future. Even in the short term, the immunity you have may not protect you against some of the new variants. There are now plenty of examples of people who have caught the virus twice, some seriously. Also, the risk of having the vaccine is tiny - about one in 100,000 according to the bigger dataset from the EU. Many things you do day in day out have a higher risk than that – driving, for example.

Could the AstraZeneca vaccine have caused my husband's blood clot?

Q: My 85-year-old husband died from a blood clot on the brain and the hospital said he had a stroke but he didn't have any symptoms of a stroke. He had his first vaccination three months ago and was due to get his second this Friday. Could the AstraZeneca vaccine have caused the blood clot?

Paul: If the clot occurred three months after his inoculation it seems unlikely there is any connection but you might talk to your GP to get their view if you have not already. It’s important to remember that clots and strokes become much more common with age and, at 85, are far from unusual.

Do you have a question about the AstraZeneca vaccine or any of the other vaccines currently in use in the UK? Leave your question below