Sunday, July 4, 2021

What does Australia’s new advice on the AstraZeneca Covid vaccine mean and what is the risk?


Australia’s vaccine rollout is facing a major shake-up after the federal government heeded the advice of its independent health expert advisory body to avoid giving the AstraZeneca vaccine to under-50s amid fears of a potential link to unusual blood clots.

The advice will have serious repercussions for Australia’s vaccine rollout strategy, given the only current alternative vaccine, Pfizer, is in low supply, and a third option, known as the Novavax vaccine, is still being considered by Australia’s drugs regulator. If approved, the federal government doesn’t see this vaccine becoming available until mid-year.

So, what triggered Thursday night’s change in position and what do we know about the risk of these blood clots?

What is Australia’s new advice on AstraZeneca?

The Australian Technical Advisory Group on Immunisation, which provides independent expert advice to the health minister, recommended adults aged under 50 receive the Pfizer vaccine as a preferred choice over the AstraZeneca vaccine.

This advice was based on a small but potentially increased risk of developing a rare and severe clotting disorder following the AstraZeneca vaccine being administered in those under 50 years.

The benefits of the vaccine still far outweigh the risk for people age 50 and above, given the serious effects – including clotting and death – Covid-19 presents to older adults especially.

What is the risk of blood clots?

The European Medicines Agency said on Wednesday night that unusual blood clots associated with low blood platelets should be listed as very rare side effects of the AstraZeneca Covid-19 vaccine. Most of the cases of these rare clots were in women under 60 years of age and occurred within two weeks of vaccination, though there have not been enough cases to confirm age and sex as risk factors.

Meanwhile the UK’s Medicines and Healthcare Products Regulatory Agency recommended people under 30 be offered a different vaccine to AstraZeneca’s, due to a very low risk of these rare clots. Most cases of these clots occurred in veins in the brain (a condition called cerebral venous sinus thrombosis, or CVST) though some occurred in veins to the abdomen (splanchnic vein thrombosis).

As of 4 April, 169 cases of CVST and 53 cases of splanchnic vein thrombosis were reported to Europe’s adverse events monitoring system. In the UK as of 31 March, 79 people had suffered CVST or splanchnic vein thrombosis, and 19 of these people died.

More than 30 million people had been vaccinated in the European Union and UK by April. It is estimated that around four people in every one million people vaccinated will experience this rare clotting, though data is still being collected and analysed, and estimates vary.

What else do we know about what causes these rare clots?

Dr Jose Perdomo, a senior research officer in the haematology research unit at the UNSW St George and Sutherland clinical school, said it appeared that the AstraZeneca vaccine triggers an immune reaction characterised by a low platelet count, and blood clotting.

Platelets are cells that usually help to stop bleeding by clumping together to form a clot. While you might think less platelets would lead to less clotting, Perdomo said in these rare clotting events a unique immune system reaction occurs involving the remaining platelets and white blood cells, and it is this reaction that makes the blood more clumpy.

This is similar to another relatively rare but serious clotting condition caused by the use of a blood thinner called heparin. In both heparin use and administration of the AstraZeneca vaccine, clotting appears within two weeks, Perdomo said.

“Clotting is seen in arteries and veins at unusual sites in the brain and abdomen and mortality is high,” he said. Mortality estimates following the clotting disorder after the vaccine have been put at between 25% and 50%. It can also lead to disability.

Why has Australia gone further than the UK, which has only stopped the vaccine for those under 30?

The risk-versus-benefit assessment for the use of AstraZeneca Covid-19 vaccine will be different for Australia compared to other countries, such as those with widespread Covid-19 transmission. This includes countries in the region such as those currently experiencing very serious outbreaks of Covid-19, such as Timor Leste, Papua New Guinea and others.

Associate professor Paul Griffin, the director of infectious diseases at Mater Health Services in Queensland said Australia could afford to be extra cautious given the low threat posed by Covid there. The difference between the benefits and risks from the vaccine was also different for younger people, he said, who are at lower risk of more significant consequences of Covid-19 such as death but may be at slightly higher – but still very low – risk of experiencing CVST and splanchnic vein thrombosis from the vaccine.

“Unfortunately no medical intervention is free of risk, and the risk of these clotting issues remains exceedingly rare,” Griffin said.

“For comparison, the oral contraceptive pill carries a risk of clotting issues [different from the rare clotting associated with the vaccine] in the order of four out of every 10,000 people taking this pill,” he said. “When assessing the risks and benefits we also have to keep in mind the risks of not vaccinating.”

But that doesn’t mean Australia shouldn’t be extra cautious given the unique position it is in with virtually no Covid circulating in the community, Griffin, who is also on the AstraZeneca advisory board, said.

It is important to note that it is not certain there is a higher risk of clotting in those under 50. A small number of cases have also been reported in older adults. While there have been more reports of the severe clotting in younger women, this may be because more vaccine doses have been given to this group because they often work in healthcare and other high-risk positions. ATAGI says in one country they examined, the rate of rare clotting was similar in men and women.

So the ATAGI advice is an extra cautious approach while it waits for more evidence.

What if I am under 50 and have a higher risk of serious consequences from Covid due to an underlying medical condition, but am told there is no Pfizer available for me?

So far no specific biological risk factors or pre-existing medical conditions have been found to increase the risk of severe clotting, including CVST, occurring after the AstraZeneca vaccine. But we know underlying medical conditions increase the risk of severe disease and death in those who are infected with Covid-19. This affects their individual benefit-to-risk balance.

ATAGI said it “respects a person’s choice to make an informed decision on whether to accept the risk of Covid-19 vaccination with the AstraZeneca vaccine”.

“ATAGI recognise that it is difficult for people to assess their personal risk where there is uncertainty about the short and long-term risk of severe Covid-19 in different age groups, and the evidence around benefit and risk of the AstraZeneca vaccine is changing quickly.”

Basically, it will come down to asking questions of your doctor and deciding if the AstraZeneca vaccine is right for you, or whether you would prefer to wait for an alternative to become available.

What if I am under 50 and already had my first AstraZeneca dose?

People who have had the first dose of AstraZeneca without any serious adverse effects can be given the second dose, including adults under 50 years. The rare clotting disorder has occurred only in the first two weeks after the first vaccine dose.

What are experts saying?

Experts including nurses, doctors and researchers are overwhelmingly saying the vaccine remains effective and safe.

An associate professor of haematology and transfusion medicine at the University of Western Australia, Matthew Linden, said: “While serious, it is important to note that the risk is rare and for more than 99.999% of people it will not be a concern.”

Prof Jonathan Carapetis, the president of the Australian Association of Medical Research Institutes and an infectious disease expert, said: “Everything we do in life – every medication we take, every vaccine we give – has a risk.”

“It is a very safe vaccine but that doesn’t mean that occasionally some very rare side effects won’t occur and that’s what we’re seeing,” he said.

“People just need to be aware that every day we balance risk versus benefit, usually without thinking about it.

“In Australia there is a one in a million chance of dying from a car crash every time you drive 400km. Based on the current data from the UK this is the same level of risk as dying from a severe blood clot from the AstraZeneca vaccine. The risk of dying from an anaesthetic in Australia is five times that, but most people wouldn’t let that put them off having surgery, even if it wasn’t urgent.”

What side effects after vaccination might indicate severe clotting?

Symptoms occur between four and 20 days after vaccination. Key symptoms of concern include severe headaches or severe abdominal pains that don’t settle with painkillers. In some cases, there may also be vomiting, confusion, neurological deficits or seizures. Anyone with these symptoms should go to the emergency department.

If I do develop this rare clotting what is the treatment?

Perdomo said the two main treatments are anticoagulants, and intravenous immunoglobulin treatment to prevent additional clotting. People should receive prompt specialist medical treatment. By recognising the signs of bloods clots and low blood platelets and treating them early, complications can be avoided.

The hospital will also order blood tests and scans.

The Thrombosis and Haemostasis Society of Australia and New Zealand have produced guidelines on detection and management of clots after vaccination, which will further improve safety.

ATAGI said: “We do not yet know to what extent earlier recognition of this syndrome and improved treatments will improve patient outcomes. More cases can be expected to occur, albeit rarely.”

What common side effects of the AstraZeneca and Pfizer vaccines shouldn’t you be alarmed about?

  • Headache

  • Fever

  • Muscle pain

  • Chills

  • Nausea

  • Mild pain

  • Redness

  • Swelling

  • Rash

How many important adverse reactions have been recorded in Australia?

For the Pfizer vaccine up to and including 28 March, there have been 33 reports of anaphylaxis [a severe allergic reaction], seven reports of bleeding disorders, six reports of facial weakness, six reports of seizure, two reports of cardiac events and two reports of loss of taste and smell. The Pfizer vaccine does not appear to carry a risk of CVST or splanchnic vein thrombosis.

For the AstraZeneca vaccine, there have been 22 reports of anaphylaxis, six reports of seizures, five reports of loss of sense of taste or smell, two reports of bleeding disorders, one report of facial weakness and one report of joint infection.

All of these are considered “adverse events of special interest” which means the TGA believes they require ongoing investigation and monitoring. It is important to remember these adverse events may not have been caused by the vaccine.

More than 855,000 doses of the vaccines have been administered in Australia as of 8 April.



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