Australian experts have voiced their support for the continued nationwide rollout of AstraZeneca’s COVID-19 vaccine, despite the European medicines regulator concluding there is a “possible link” between the jab and a number of rare blood clots.
The European Medicines Agency (EMA) found in its preliminary review that while the overall risk of clotting in people who’ve been vaccinated is on par with the general population, it could not rule out a potential link with a number of rare clots associated with low blood platelets.
These rare clots were almost all in women under 55, a group that is typically not at a high risk of clotting.
However, the EMA said the benefits of the vaccine “still outweigh the risks”.
RECAP: Look back on the latest news on the COVID-19 pandemic.
University of Adelaide associate professor in virology Farhid Hemmatzadeh said even considering the investigation’s findings, if he was given a list of every COVID-19 vaccine candidate available, he would still pick the AstraZeneca option.
“The Oxford AstraZeneca vaccine is the safest vaccine that exists in the vaccine list,” he said. 
Even so, 25 cases of rare clots in 20 million vaccinations across Europe has seen a number of countries suspend their AstraZeneca rollouts out of caution, and prompted the EMA to investigate.
Here’s what we know about their findings.
Europe, blood clots and an investigation
So you have questions about the COVID vaccines? We have answers
Confused about Australia’s vaccine rollout? We’ve tracked down the answers to the questions you’ve been asking.
Read more
A blood clot is when a clump of blood changes from a liquid to a semisolid state, and most of the time they’re harmless.
Post-vaccination, the EMA found a number of “very rare cases” of “unusual blood clots” were reported in patients who also had low levels of blood platelets (which help the blood clot)  and that the majority of these cases were in women under 55.
The regulator launched its review into the jab after 13 states across Europe suspended use of the vaccine over fears of a link to blood clots.
The review specifically investigated seven cases of blood clots in multiple blood vessels right throughout the body (DIC) and 18 cases of cerebral venous sinus thrombosis (CVST), nine of which resulted in death.
Again, most of these very rare cases of DIC and CVST occurred in people under 55, and the majority were women.
Dr Hemmatzadeh said there was no “scientific connection” between the risk of rare blood clots and younger women, although more research was needed.
“It could be accidentally or it could be related to some other issues, like the genetics or the blood disorders, or whatever the sex or the race of those particular people could be,” he explained.
“It’s not been fully investigated, and it’s not clear for anyone why it’s happening.”
And Queensland University of Technology emeritus professor Gerry FitzGerald explained that because the incidence of these “unusual” cases was so low,  the EMA ruled that the risk of contracting COVID-19 “far outweighed” the risk of vaccination.
What did the report find?
The EMA’s review found that the number of blood clots (469 reports, 191 in Europe) reported after the vaccination was “lower than that expected in the general population”, leading it to conclude that there’s no “overall risk of blood clots” related to the AstraZeneca jab.
Its four main findings were that:

  • The benefits of the AstraZeneca vaccine outweigh the risk of side effects
  • The jab is not associated with an increase in the overall risk of blood clots
  • There’s no evidence that there’s a problem with specific batches or manufacturing sites
  • The vaccine may be associated with very rare cases of blood clots associated with low levels of thrombocytopenia

This means that while the overall number of blood clots in people who have been vaccinated with AstraZeneca wasn’t higher than in the general population, there could be a link between the vaccine and some very rare cases of blood clots associated with thrombocytopenia (a condition associated with a low blood platelet count).
LoadingDr FitzGerald said there was a “paradox” in these rare reports.
“The paradox, of course, is that if you have low blood platelets, you’re more likely to bleed rather than clot,” he explained.
“So if there is an association, it’s probably a complicated immunological association, but the cases are so rare that they seem to have reached the conclusion that we can’t disprove it, so we’re going to continue to monitor it.”
Dr FitzGerald also said that DIC “consumes the platelets” in a patient, causing platelet levels to drop.
“It’s clotting everywhere so the platelets are being sucked up to form the clots,” he said.
“So the more complicated question is: ‘does this complication occur in people that have low platelets, or does this compilation occur and therefore those people have low platelets?”
The regulator flagged that more research was needed.
“A causal link with the vaccine is not proven, but is possible and deserves further analysis,” the review concluded.
Read more about COVID-19 vaccines:
Virologist and clinician Lara Herrero from Griffith University’s Institute for Glycomics said all people with clotting disorders and low platelet count should discuss their personal position with their doctor before getting vaccinated.
“As would be the case for this group in any medical situation. In almost all cases medical doctors will deem the vaccine safe,” she said. 
“For high-risk people, it may be worth obtaining baseline bloods to ensure normal platelets prior to vaccination.”
What are the implications for Australia?
AstraZeneca is the vaccine most people in Australia will get, with 50 million doses to be made on home soil.
LoadingIt’s a viral vector vaccine that enlists the help of a harmless chimpanzee adenovirus to deliver a payload of genetic material in the form of DNA into our cells.
Our own Therapeutic Goods Administration (TGA) has already come out in support of the vaccine, insisting there’s “no evidence” the AstraZeneca COVID-19 vaccine is the cause of blood clots.
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 clots.
Dr FitzGerald said he still backed the vaccine’s rollout in Australia, even with the nation’s low overall number of COVID-19 cases.
“Ultimately, this pandemic is not over until it’s over everywhere,” he said.
Health in your inbox
Get the latest health news and information from across the ABC.
Dr Hemmatzadeh said he was still confident in the jab’s safety, and any policy decision to stop giving the AstraZeneca option to women under the age of 55 would be too early at this stage.
“There is no proven link between any particular age, any particular sex, or any particular race in terms of hypersensitivity,” he said. 
“We have no risk-free vaccine in the world, all of the vaccines we use in general have some risks.”
Dr Herrero also voiced her support for the AstraZeneca option, and said there was “no need” to offer the Pfizer jab to women under 55.
“We should continue to provide whatever vaccine that is safe and effective and available,” she said.
“This means that we should be continuing to provide the AstraZeneca vaccine to women under 55.
“I am a female under the age of 55. I would take the AstraZeneca vaccine and I would advise my loved ones in the age group to do the same.”
Dr Herrero said people should be told about all of the vaccine’s possible side effects prior to getting the jab, including these potential unconfirmed  findings.