AstraZeneca’s vaccine rollout has been paused across Europe amid blood clot reports. Should Australia follow suit?



Australia’s medicines regulator insists there’s “no evidence” the AstraZeneca COVID-19 vaccine is the cause of blood clots which has seen its use suspended by several leading European nations, including Germany and France.

Chief medical officer Paul Kelly said while he was aware of countries in Europe pausing rollout of the vaccine, other countries, including Canada and the UK were still continuing to use AstraZeneca as planned.

“With a vaccine rollout like this, we need to monitor carefully for any unusual events,” Professor Kelly said.

“The Australian Government remains confident in the AstraZeneca COVID-19 vaccine and there is currently no evidence that it causes blood clots.”

The AstraZeneca vaccine is the jab most people in Australia will get, with 53.8 million doses of the AstraZeneca secured by the Department of Health.

But what exactly are blood clots? Are the numbers we’re seeing in vaccinated populations higher than expected? And should Australia halt its rollout of the AstraZeneca vaccine?

A healthcare worker holds the COVID-19 AstraZeneca vaccine.
Australia’s regulator insists there’s “no evidence” the AstraZeneca COVID-19 vaccine is the cause of blood clots.(Getty Images: Antonio Masiello)

What are blood clots?

In the simplest terms, a blood clot is when a clump of blood changes from a liquid to a semisolid state.

Most of the time, blood clots are totally harmless and can be really useful if you scratch yourself and they can prevent you from losing too much blood.

But if a blood clot forms in your veins, it can travel to your organs and stop blood flow — leading to potentially deadly consequences.

The Therapeutic Goods Administration (TGA) says venous thromboembolism (VTE), a clot which starts in the vein, is the third-most common cardiovascular disease in the world — with more than 10 million reports a year.

People who are over the age of 65, smoke, have cancer, are pregnant or have a family history of blood clots are more at risk of getting them.

In Australia, at least 17,000 people annually — roughly 50 people every day — develop VTE. So far, there have been no reports of blood clots following the vaccine’s rollout in Australia.

In a statement, the TGA said it had not seen any evidence of a “biologically plausible relationship” that would suggest a cause-and-effect relationship between the vaccines and blood clots.

More than 17 million people have been vaccinated with the AstraZeneca vaccine across Europe and the United Kingdom, and there have been 15 reports of deep-vein thrombosis and 22 of pulmonary embolisms following vaccinations.

The European Medicines Agency has also said there is no indication that blood clotting issues were caused by the vaccination, a view echoed by the World Health Organization.

And according to AstraZeneca, a review of safety data of people vaccinated with its COVID-19 vaccine has shown no evidence of an increased risk of blood clots.

Professor Griffin described the suspension of the vaccine in parts of Europe as an “overreaction”.

“In my opinion, this response is an overreaction and while this is perhaps how these countries prefer to respond, we should make sure we don’t overreact in our country and that we continue to make evidence-based decisions based on the available data at hand,” he said.

“This vaccine has proven very safe and effective in large clinical trials.”

‘It’s too early to be worried’

Coronacast co-host Norman Swan said although the rate of blood clots in the vaccinated population was lower than the background rate, the “worrying thing” was that there had been a number of reports of younger people with clotting.

“Age is a risk factor — the older you are, the more likely you are to get clots,” he said.

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Dr Norman Swan says issues surrounding AstraZeneca vaccine are complicated

Dr Swan also explained that some people who had presented with blood clots also had low levels of platelets — cells which help blood to clot.

“It’s just possible that the vaccines as a whole have a problem with creating antibodies in some people to the platelets and paradoxically causing blood clots,” he said.

Theoretically, platelet levels could drop because of a blood clot in the lung.

Professor Griffin said although young people were less likely to get blood clots, it wasn’t without precedent and the number of people who had them after being vaccinated was still very small.

“We do still see people in those [younger] demographics who very occasionally get blood clots,” he said.

When questioned about the low platelet levels some people had presented with, Professor Griffin said while it wasn’t common, it wasn’t necessarily cause for alarm.

“We do see that in populations from time to time,” he said.

“It’s too early to be worried about these numbers.”

Should Australia halt its rollout?

No, according to our experts. Although, they say there is a need for more research and monitoring of the situation.

“If it is linked to the vaccine, which is very unlikely, it may be that there’s a group of people who should not get the vaccine … it’s got to be taken seriously.”

Nigel Crawford, director of a vaccine safety and clinical immunisation research group based at Murdoch Children’s Research Institute, urged “extreme caution in pausing rollouts” while investigations were underway.

“Because once a vaccine rollout is paused, it can sometimes dent vaccine confidence so much that it struggles to recover, as seen in Japan with the human papillomavirus vaccine,” Dr Crawford said.

Robert Booy, senior professorial fellow at the National Centre for Immunisation Research, added that Australia had an “excellent system” for the surveillance of rare events, such as blood clots, which can occur after vaccination.

“The issue of blood clots appearing to occur after use of the AstraZeneca COVID vaccine is being taken very seriously and is being carefully investigated,” he said.

“The data collected so far suggests that blood clots are not occurring any more often than would be expected by coincidence.”

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