COVID vaccine blood clot facts: Experts explain how AstraZeneca jab works

It’s the bogeyman making Aussies think twice about getting a COVID-19 jab. Here, experts explain the facts about blood clots.

It’s the bogeyman that’s making Australians think twice about getting their COVID-19 jab – TTS blood clots.

To date, 24 Australians out of the 2.1 million who have received the AstraZeneca jab have had a confirmed or suspected case and one, a 48-year-old woman, has died.

Here we talk you through the condition, how to spot it, how it’s treated and how small the risk actually is.

What is TTS?

TTS is short for thrombosis with thrombocytopenia syndrome a rare blood clotting condition that has been linked to AstraZeneca’s COVID-19 vaccine.

It happens when small blood cells called platelets that help the blood clot fall below normal levels, a condition called thrombocytopenia.

Although this condition usually reduces the blood’s ability to clot, it can sometimes cause clots to occur when they shouldn’t.

The head of Australia’s medicines watchdog the Therapeutic Goods Administration Professor John Skerritt said it’s thought the condition is brought on by a wayward immune response to AstraZeneca’s COVID-19 vaccine.

Therapeutic Goods Administration Professor John Skerritt. Picture: NCA NewsWire / Gary Ramage

The most dangerous of these clots appear in the in the brain when the platelets stick together and cause a blockage that prevents blood draining out of the brain causing damage similar to a stroke.

The clots can also form in the gut, the legs and other parts of the body.

“People who have had other blood clots have no risk increased risk, it’s not associated with whether you have had clots before or whether you’re on anti- coagulants or platelet medicines or whether you’ve had a cardiac stent or a stroke,” Professor Skerritt said.

What are the symptoms?

Symptoms include headache, tiny red spots under the skin, blurred vision, fainting or loss of consciousness, loss of movement in parts of the body, or coma, stomach ache, a cold feeling in the leg or a swelling in the leg.

These typically appear 4-20 days after the vaccination.

It’s worth remembering COVID-19 itself causes thrombocytopenia in around four in ten people and up to 95 per cent of those with severe disease.

How rare is TTS?

TTS is very rare, only one in every 100,000 people who get the AstraZeneca jab will develop the condition. That is the same as saying if every seat at the MCG was filled with people who’d had the vaccine one person would develop a blood clot.

Every day 50 Australians develop blood clots that are not related to vaccination and there is an almost one in 12 risk of developing a blood clot at some stage throughout life.

You are much less likely to get TTS from the jab than you are to get a blood clot from the contraceptive pill where the risk is one in every 1,000.

Although the risk of dying from TTS (25 per cent) is higher than from a clot caused by the pill (3 per cent).

Many every day medicines are killers but we give barely a thought to using them.

Paracetamol for example killed over 200 people in the ten years between 2007 and 2017.

One of the most commonly used prescription medicines in Australia- atorvatstain has been linked to 13 deaths.

The chance of being killed on the roads is five times higher than getting a blood clot from AstraZeneca’s vaccine.

Why then have experts suggested its safer for people aged under 50 to have the Pfizer vaccine?

The risk of TTS syndrome reduces with age and for people under the age of 50 the risk of the rare blood clots is 2 in 100,000, if you are aged 50-70 its 1 in 100,000, if you’re over 70 it drops to 0.5 per 100,000.

On the other hand, the risk of dying or getting severely ill from COVID increases with age.

“For example, if you’re 70, you’re three to six times more likely to be hospitalised with COVID than if you’re 30, you’re up to 10 times more likely to go to ICU and you’re many fold times more likely to die of COVID, compared to a 30 year old,” A/Professor Blythe said.

This is the reason experts picked 50 as the threshold age at which the risk of the blood clots was outweighed by the risk of death or severe disease.

“A statistic that’s quite sobering is the fact that 99.5 per cent of all deaths in Australia, from COVID have been in the over 50s even though the main age that has got COVID are those aged 20 to 29,” Professor Skerritt said.

The risk of TTS syndrome reduces with age.

Should you be worried about the blood clots?

The reason we’re having COVID-19 vaccines is to save lives so a vaccine side effect that actually takes lives is a risk that has to be taken seriously.

That’s why our medicines watchdog the Therapeutic Goods Administration (TGA) has said the Pfizer vaccine, which does not have a blood clot risk, is the preferred vaccine for people aged under 50.

“We want people to know that if this does occur, they should present and get treatment and by alerting people that means that we may be detecting milder cases,” the co-chair of the government’s vaccine advisory body Associate Professor Chris Blythe said.

Associate Professor Chris Blythe. Picture: University of Western Australia.

What are the tests for TTS?

If you think you may have a TTS blood clot doctors order a blood test for a specific protein that’s produced by the body to break down clots called D dimer.

They will also test for anti-PF4 antibodies that activate platelets, they will also check the condition is not linked to your use of the blood thinning drug heparin given to most Australians if they are undergoing surgery.

What are the treatments?

Patients will be given intravenous immunoglobulin, which helps boost the immune system and reduce the effects of inflammation.

They may also be given a synthetic anticoagulant that prevents further clotting.

“The main thing you want to do is prevent further clotting, and to get that clot out of the way where it might go to the brain or the lungs or whatever,” Professor Skerritt said.

People will be hospitalised for a few days for observation while the clots dissolve.

“We don’t know if there are long term effects because this condition was really only described last month, it was just around Easter when the first cases of this were reported so we don’t know what it looks like in six or eight months,” Professor Skerritt said.

“But we’re seeing that people’s platelets and circulation are restoring towards normal. We don’t have any evidence that the people who have recovered shouldn’t live a full and healthy life,” he said.

Originally published as COVID vaccine blood clot facts: Experts explain how AstraZeneca jab works