Safety of COVID-19 vaccine by AstraZeneca explained: Blood clot cause, risks, chance of death and benefits

Nine days after getting an AstraZeneca jab, a young and otherwise healthy NSW woman died. Should you be worried about the safety of COVID vaccines?

The death on Thursday of a 48-year-old woman from New South Wales, who developed serious clotting very soon after receiving the AstraZeneca vaccine, has again raised serious concerns about its safety.

Authorities are racing to investigate the exact cause of her death, which occurred in the intensive care unit of John Hunter Hospital, five days after her first dose.

She was reportedly a diabetic but in otherwise good health.

While the government has changed its advice, that people under 50 should not get the jab, its deployment continues among older and vulnerable populations.

Earlier this month, authorities in Europe confirmed a causal link between the vaccine and very rare but serious blood clots.

This is based on several dozen people developing them shortly after receiving the first dose – a condition scientists have labelled “vaccine-induced prothrombotic immune thrombocytopenia”, or VIPIT.

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What is VIPIT and how dangerous is it?

As the name suggests, VIPIT is a kind of thrombocytopenia, which is the medical term for clotting.

A cohort of immunology, medicine and public health experts from Victoria University – Associate Professor Anthony Zulli, Professor Maximilian de Courten, Vasso Apostolpoulos and Maja Husaric – explained the condition like this.

“Thrombocytopenia is a condition whereby the numbers of thrombocytes – very small blood particles, or platelets – are markedly reduced,” they wrote in an article for The Conversation.

“Platelets form clots to stop bleeding, so when you don’t have enough platelets in your blood, your body can’t form clots. This can lead to excessive bleeding.”

Possible symptoms range from the mild to the serious, including severe headaches, seizures and visual changes, and abdominal pain.

“In rare cases of thrombocytopenia, clots can develop in the vessels draining blood from the brain,” Associate Professor Zulli and colleagues wrote.

That’s called cerebral venous thrombosis, or CVT, and forms in the venous sinuses of the brain – a system of veins between its tough outer layer, just below the skull.

It can block blood draining from the brain towards the heart, causing cells to break and seep into tissue, potentially leading to stroke.

Obviously, that’s quite dangerous and required critical medical care.

As of last week, the European Medicines Agency had received 170 reports of CVT in people who received the AstraZeneca shot.

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Many countries, Australia included, do not recommend AstraZeneca’s vaccine for younger people. Some countries have suspended its use entirely. Picture: AFP

What’s happening with the AstraZeneca vaccine?

As Associate Professor Zulli and his colleagues explained, the vaccine developed by AstraZeneca simulates antibodies to mount a defence against the virus, specifically by attacking its spike protein, or the thing COVID-19 uses to attach to cells in the body.

“But in some people, the AstraZeneca vaccine seems to produce antibodies that react with platelets, making them stick together, leading the blood to clot,” they wrote.

“This in turn reduces circulating platelet numbers, and hence the thrombocytopenia.

“These antibodies are similar to those found in some people on a blood thinning drug called heparin. The immune response to heparin generates antibodies that bind to platelets.

“This can lead to blood clots in some people, called heparin induced thrombocytopenia. As many as one in 20 patients receiving heparin develop thrombocytopenia.”

It seems that VIPIT occurs between four and 20 days after a person receives the AstraZeneca jab.

As for why, that’s something experts around the globe are urgently trying to figure out.

Is it a rare side-effect?

In terms of the COVID-19 vaccine, VIPIT is an extremely rare side-effect.

Analysis of data by the Thrombosis and Haemostasis Society of Australia and New Zealand put the chances of VIPIT at about one in 500,000 people who’ve received the AstraZeneca vaccine.

In Australia, there have been two reported cases of blood clotting among the 700,000 recipients of the AstraZeneca vaccine.

Data out of the US puts the risk of naturally occurring blood clots at one in 30,000 adults every year.

A report released by the UK’s Medicines and Healthcare Products Regulatory Agency (MHRA) last week broke down the latest available data, as of March 31.

More than 20 million doses of the AstraZeneca jab had been given at that time, and 79 cases of blood clots had been reported.

That’s about one in 250,000 people, or four in a million, at risk overall.

Of the 79 cases, 44 developed CVT and 35 had thrombosis in other major veins. Sadly, 19 people died.

Dr June Raine, chief executive officer of the MHRA, said: “No effective medicine or vaccine is without risk.”

In fact, the condition can be sparked by some 300 common medicines, from the contraceptive pill to penicillin and over-the-counter painkillers.

Who’s most at risk?

It must be stressed that the number of cases of clots is extremely small in the scheme of things, and so conclusions are far from concrete.

Women under the age of 65 have predominantly been impacted. It also seems that there are issues with the first dose only – not the second.

Instances of blood clotting is less likely in older groups, the data suggests.

For example, based on the UK reports, for those in their 60s and above who get the AstraZeneca jab, 0.2 people per 100,000 are at risk of VIPIT.

By comparison, we know that for every person in that age bracket who develops a clot, another 70 will wind up in intensive care in a month from COVID-19 infections.

Some nations hard-hit by COVID-19 are pushing ahead with the rollout, saying the benefits far outweigh the very rare risk. Picture: Getty Images

What else can cause this kind of response?

Much has been said in recent weeks about the significantly higher risk of clotting from the contraceptive pill.

Experts estimate about one in 10,000 women who take birth control will develop a blood clot, which is obviously a significantly higher risk.

Pregnancy also carries a high risk of blood clots, with women carrying a child five times more likely to develop them than those who aren’t pregnant.

Smokers are also more likely to suffer clots, while minimal movement over long periods of time – such as on long-haul flights – also comes with high risks.

Associate Professor Ben Chan, an expert in global health at the University of Toronto, told Global News the chances of getting a blood clot after an AstraZeneca jab is the equivalent of being hit by a car and dying.

“Yes, these are risks, we should be aware of them, but we need to put them into perspective compared to the daily risks that we have in our lives around us,” he said.

“Just about every medication that we take has some potential for side effects, and all those medications have great advantages to us. They help us keep alive.”

In fact, a COVID-19 infection itself is significantly more likely to cause blood clots than the AstraZeneca vaccine, a study has found.

Researchers at Oxford University – that’s where the vaccine was developed, but these scientists aren’t affiliated with that department – determined the risk is about eight times greater.

“There’s no doubt that COVID is a much greater risk of this (clotting condition) than any of the vaccines,” Professor Paul Harrison, a co-author of the study, said upon its release on Friday.

What about the risk of death?

The risk of developing VIPIT after having an AstraZeneca vaccine is extremely rare – but the condition itself is also very serious.

Based on reports so far, about 25 per cent of those who have developed VIPIT have died, Associate Professor Hassan Vally from La Trobe University said.

“To put it in perspective, this puts the risk in the same order of magnitude to the average risk of dying if you complete a marathon, go scuba diving, or rock climbing,” he wrote for The Conversation.

Do the benefits outweigh the risks?

When reports first emerged about a potential link between the AstraZeneca jab and blood clots, authorities in most parts of the world insisted the benefit of the jab outweighed its risk.

That remains largely the case, although some countries have entirely suspended the rollout of the vaccine for younger people.

But, based on the data from overseas, it’s still true that the benefit from avoiding potential illness or death from a COVID-19 infection significantly outweighs the very rare identified risks of the AstraZeneca vaccine.

“We make these sorts of calculations every day in all aspects of our lives,” Associate Professor Vally said.

“When we decide to get in the car, we know there’s a risk associated with driving. But we assess the risks are worth taking as the benefits of getting where we want to go quickly are worth it.

“Mostly, we make these calculations without being consciously aware we’re doing it. Sometimes the parameters underlying these calculations are easy to grapple with — but sometimes they’re more nebulous.”

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Cambridge University analysis of the risk versus benefit for each age group.

However, Associate Professor Vally said weighing up the risk isn’t simple, nor black and white, and depends on a range of factors – including age, health, seemingly gender, and where you live.

“While it’s all well and good in some countries to say you’re more likely to get very sick with or die from COVID than experience a complication from the vaccine, in Australia we have next to no COVID, so the risk of adverse outcomes from COVID is much lower,” he said.

“This needs to be factored into the equation.

“We also have different strains of the virus, which can vary in how infectious they are and how sick they might make you. This also needs to be added to the mix.”

What are the implications?

We’ve already witnessed the consequences of the very rare but serious risk of blood clotting from the AstraZeneca COVID-19 vaccine.

The Federal Government shifted its advice last week, that Australians aged under 50 for the most part should avoid getting the jab and instead wait for the Pfizer vaccine.

Australia has put most of its eggs in the AstraZeneca basket, relying on the local mass production of doses to provide what’s needed to inoculate the population.

Now that millions of people won’t be getting it, the rollout is significantly delayed and all former targets have been abandoned.

Ordering more Pfizer doses is tricky due to extremely high global demand – a top-up for 20 million more jabs was rushed through last week, but it’s not close to being enough.

On top of that, actually getting the supply onto Australian shores is even harder because there simply aren’t any to ship here.

Those Aussies hoping for a shot in the arm sooner rather than later will be disappointed.

The government says AstraZeneca remains an important part of Australia’s vaccine rollout. Picture: AFP

When it comes to those aged over 50 who are still encouraged to get the AstraZeneca jab, there’s now a risk of low confidence about its safety, Professor Adrian Esterman, an epidemiologist at the University of South Australia, said.

“The government needs to reinstate confidence and convince over 50s the AstraZeneca vaccine is safe,” he wrote the The Conversation. “This will require a major effort using Australia’s best marketing brains.”

The government also needs to get cracking on approving another vaccine, developed by US biotech firm Novavax, which is in final stage trials now and shows strong efficacy, he said.

“This would safeguard us against any further issues with the AstraZeneca vaccine, and the Novavax could eventually replace AstraZeneca because of its much higher efficacy.”

Australia has ordered 51 million doses of this jab, but it won’t arrive until the end of the year – and it still needs Therapeutic Goods Administration approval.

What should you do?

To start with, if you’ve already had the first dose of the AstraZeneca vaccine without any adverse effects, experts unequivocally agree that you should have the second.

As with all matters related to personal health and wellbeing, you should seek the advice and guidance of your GP about what vaccine is right for you.

For example, the government advice for people under 50 to get the Pfizer jab instead does not include people with pre-existing medical conditions or who are part of other vulnerable populations.