Everything women need to know about the AstraZeneca vaccine

In recent weeks, concerns have been raised about the safety of the AstraZeneca vaccine due to its potential link to blood clots.

Today, the Medicines and Healthcare products Regulatory Agency (MHRA) announced that people under the age of 30 will be offered a Pfizer or Moderna vaccine instead of an AstraZeneca jab, after the  regulator found a possible link to blood clots in young people. 

Dr June Raine, chief executive of MHRA, said the risk of the rare side effect of blood clots “remains extremely small”. Up to March 31, the vaccine had been administered roughly 20 million times. 79 people in the UK presented with a blood clot, and 19 people have died. Of the 79, 51 were women and 28 were men, she added. 

Professor Sir Munir Pirmohamed, chair of the Committee of Human Medicines (which advises the government on the safety of medicines), said pregnant women and people with a history of blood clots should speak to their doctor to see if the benefits of having an AstraZeneca jab outweighs the risks.

The news comes after several European countries, including Norway, Austria, Iceland and Italy, suspended the roll out of the vaccine. Germany has temporarily limited the use of the AstraZeneca jab for people below the age of 60, after the medicines regulator found 31 cases of a type of rare blood clot among nearly 2.7 million people who had received the vaccine in Germany. Most of these were women. 

However, experts around the globe have stated that the vaccine is safe for use and, that at this stage, there is no causal link between blood clots and the jab. Boris Johnson has supported their statements and received his first dose of the AstraZeneca vaccine last month.  

The benefits of the Oxford/AstraZeneca vaccine continue to outweigh any risks for most people, the UK medicines watchdog has said, as European regulators ruled that unusual blood clots were “very rare side effects” of the jab.

Why are there concerns?

Many countries are concerned about the AstraZeneca vaccine’s potential link to blood clots. 

The first countries to raise concerns over the vaccine were Norway and Austria. A person in Austria died 10 days after they received the vaccination, after being diagnosed with blood clots. Another was hospitalised with pulmonary embolism (blockage in arteries in the lungs) after being vaccinated. However, Denmark became the first country to suspend the vaccine altogether, as someone died after they had received the jab.

The German medicines regulator, the Paul Ehrlich Institute, has found 31 cases of cerebral sinus vein thrombosis (CSVT) – clots forming in veins that drain the brain – among people who received AstraZeneca in Germany. Almost all the cases are reportedly in younger and middle-aged women.

What do experts say about the link between the vaccine and blood clots?  

The EMA and the World Health Organisation (WHO) undertook a review of the evidence around blood clots and the AstraZeneca vaccine in March. Both organisations established that there is no evidence that there is a link between the vaccine and blood clots, and have actively encouraged other countries to continue using it. Dr Hans Kluge, WHO senior director, echoed this idea, saying that the benefits of the AstraZeneca vaccine “far outweigh the risks”.

Speaking at the MHRA announcement on April 7, Professor Jonathan Van-Tam labelled the decision to offer under-30s a non-Astra vaccine a “course change”, and emphasised that “vaccines continue to be the way out for the UK”.

“If you sail a massive liner across the Atlantic it is not really reasonable that you are not going to have to make one course correction over that time,” he said.

Previously, experts have pointed out that blood clots are fairly common: because the roll out of the vaccine is still in the early stages, it is tricky to distinguish between causal effect and coincidence. Professor Stephen Evans, of the London School of Hygiene and Tropical Medicine, has said: “This is especially true when we know that Covid-19 disease is very strongly associated with blood clotting and there have been hundreds if not many thousands of deaths caused by blood clotting as a result of Covid-19.”

Why are more women experiencing blood clots?

Most of the blood clots that have been observed so far have been in women under the age of 65. Experts aren’t entirely sure why this is, but research into the topic is underway.   

One theory is that this demographic makes up most of the vaccinated population. Early clinical trials of the AstraZeneca vaccine included very few older recipients, so many countries decided to use the vaccine on people younger than 65. In practice, this meant that the vaccine was rolled out among priority groups, such as healthcare workers and teachers – professions which are mostly made up of women. Sara Viksmoen Watle, chief physician at the Norway Institute of Public Health, said that in Norway 78 per cent of the AstraZeneca doses went to women. 

In the UK, the vaccine was first given to the older population. In March, it was reported that the UK had five incidences of blood clots in people who have had the AstraZeneca vaccine, although the medicines regulator said that no causal link had been made with the jab. A recent study published by Swansea University found that no cases of blood clots have been found in more than 440,000 people who have been vaccinated against coronavirus in Wales.

How does the risk of blood clots compare between the Pill and AstraZeneca?  

Some women have commented that the risk of blood clots from the AstraZeneca vaccine is lower than that of the contraceptive pill. A study published in The Lancet suggests that – excluding other factors such as weight and smoking habits – there is three times the risk of blood clots for women who take the contraceptive pill. The risk increases for pills that contain higher levels of oestrogen. According to the National Blood Clot Alliance, this equates to around one in 1,000 women per year. That’s why doctors don’t recommend that women take birth control pills if they have a history of blood clots, heart attacks or strokes.

So how does this compare to the risk from the AstraZeneca vaccine? The risk of developing a blood clot from the contraceptive pill is significantly higher. If you compute the numbers announced during the MHRA press conference, the risk of rare blood clots is roughly four in one million.

Is it safe for women to have the AstraZeneca  vaccine?

Speaking before the MHRA announcement, Simon Clarke, an associate professor in microbiology at the University of Reading, said women should not be concerned about receiving the AstraZeneca vaccine. “The numbers are so small that it is really impossible to point to any difference in the number between men and women as being significant. When you have small sample sizes, one or two increases in either direction can give you a false impression.” 

He added that the risk of developing a blood clot from going on a plane, or taking the contraceptive pill, are currently far higher and the risk of having the vaccine remains “much less” than that of contracting the virus. 

Professor Beate Kampmann, of the London School of Hygiene and Tropical Medicine, agreed. She explained that the clots that have caused alarm in Germany are rare “manifestations of an auto-immune condition which affects activation of platelets in the blood”. These are the types of blood cells that make our blood clot if we have a cut, which can lead to clots in the brain.

“At the moment, other than the age group concerned, which appears to be pre-menopausal, we don’t have detail on whether these women might have in any way been predisposed. Although this rare condition has now been added to the labelling of the AstraZeneca vaccine, it is obvious that it is extremely rare and that the benefits of the vaccine on a population level far outweigh the risks,” she said. “Covid itself can cause blood clots, and many more serious complications of Covid continue to be prevented by the vaccine.”

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