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AstraZeneca or Pfizer? Australia's COVID-19 jab confusion

This article was published on
July 1, 2021

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AstraZeneca can now be requested by anyone under age 40 in a major change to the vaccine program announced by Prime Minister Scott Morrison on Monday. The decision has not been backed by the Australian Medical Association, and in addition, the advice from the independent Australian Technical Advisory Group on Immunisation – that Pfizer is the preferred vaccine for under-60s due to an increased risk of rare clotting events linked to the AstraZeneca jab – is unchanged. Queensland Premier Annastacia Palaszczuk and WA Premier Mark McGowan have both spoken out against advice issued by the PM, saying they do not believe the under-40s should be given the AstraZeneca vaccine. Further, Health Minister Greg Hunt reiterated in a press conference today that the medical advice surrounding vaccines has not changed, but the AstraZeneca vaccine can be used in adults under 60 for whom Pfizer is not available. Below, Australian experts weigh in on the confusion.

AstraZeneca can now be requested by anyone under age 40 in a major change to the vaccine program announced by Prime Minister Scott Morrison on Monday. The decision has not been backed by the Australian Medical Association, and in addition, the advice from the independent Australian Technical Advisory Group on Immunisation – that Pfizer is the preferred vaccine for under-60s due to an increased risk of rare clotting events linked to the AstraZeneca jab – is unchanged. Queensland Premier Annastacia Palaszczuk and WA Premier Mark McGowan have both spoken out against advice issued by the PM, saying they do not believe the under-40s should be given the AstraZeneca vaccine. Further, Health Minister Greg Hunt reiterated in a press conference today that the medical advice surrounding vaccines has not changed, but the AstraZeneca vaccine can be used in adults under 60 for whom Pfizer is not available. Below, Australian experts weigh in on the confusion.

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What our experts say

Context and background

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Media briefing

Media Release

Expert Comments: 

Professor Robert Booy is an infectious diseases and vaccine expert with an honorary professorship at the University of Sydney, is a director of the Immunisation Coalition and is a consultant to vaccine manufacturers.

Suppose you’re a 25-year-old young person, male or female. How do you weigh up the risks of catching COVID, and the complications of that, with the risk of having a COVID vaccine, Pfizer or AstraZeneca?

First of all, we know that COVID is less severe in young adults and the risk of hospitalisation or death from COVID is much lower than an older person.

So, what is needed is a way in which to calculate a risk-benefit ratio that’s relevant to you, as a young person. Such a calculator is available on the web from the UK. It was set up by the Oxford group. It’s extremely helpful if you live in the UK where disease is common but we need a risk calculator for Australian circumstances.

Several groups are working on just that. For example, the immunization coalition is in discussion with the Oxford group to quickly adapt their instrument to Australia. Watch this space.

So a 25-year-old person has to consider if they have Pfizer, having to wait for some weeks and months, or getting AZ quite quickly.

She/he would take into account that there is an imminent risk of transmission if living in the eastern suburbs of Sydney, but a very low risk in many other parts of Australia.

And understandably would be concerned that there is a risk of clotting syndrome (TTS) in the order of 1 in 25,000 after the first dose of AstraZeneca.

The clot problem would probably require hospitalisation but only about one in 25 people hospitalized might die from it, giving a risk of less than 1 in 500,000 of dying from a clot due to the vaccine. That’s about the same risk as being struck by lightning. Also the risk of being killed from a motor vehicle accident is much higher, and the risk of getting a serious clot in a 25-year-old woman on the oral contraceptive pill is quite a bit higher.

No vaccine or medicine is without some risk, albeit rare, or even very rare. Reports from the United States suggest that the Pfizer jab may result in a risk of myocarditis/pericarditis in one out of 100,000 vaccine recipients, with a higher rate if you are young and male.

Also, about one in 100,000 people given an mRNA vaccine is at risk of anaphylaxis but the allergic reaction is most unlikely to cause death.

There’s a lot to consider. Experts are working on it, and these calculators will hopefully be available soon.

In the meantime, GPs are well equipped to answer people’s questions, their opinions are respected and the government is supporting GPs to have enough time to undertake meaningful discussions with their patients about vaccinations.

Professor Christine Jenkins

Why is the AMA disagreeing with Scott Morrison’s decision to make the AstraZeneca vaccine available to under-40s?

"The AMA appears to be risk-averse in this situation. Doctors don’t want to be exposed to negligence claims and lawsuits, and so the AMA prefers to recommend that doctors line up with ATAGI’s advice. This means they defer to a higher authority and it protects them at the same time. However, it doesn’t mean that it is in patients’ best interests nor in the wider community’s interests. A different assessment of risk could be done using a different risk profile – one not based on comparing probability of ICU admission vs TTS. This risk analysis would compare the risk of transmission, getting the disease at all, losing time from work and infecting your family and friends to risk of TTS. These are far more likely events than ICU admission which is rare and an uncommon event for people under 50 years old. An analysis that includes more common but troubling events for under 50 year olds, weighs up wider community benefit and is not shackled by the issues ATAGI has said it has taken into account would be likely to demonstrate a far more persuasive case for the AZ vaccine."

Should young people be getting the AstraZeneca vaccine or wait for the Pfizer?

"Do young people want to be exposed to viral illness risk at all – not just ICU admission, but days of feeling very unwell, time off work sick, risk of long COVID, possibility of transmitting the virus to their children? Do they want to risk transmitting it to their parents – many of whom are older and have chronic diseases that make them very vulnerable to hospital admission, ICU admission and death? NO!! Young people should get vaccinated and if the AstraZeneca vaccine is the only one they can get now, then they should go for it. This will bring many of them up to being around 50 per cent protected from symptomatic COVID very quickly, reduce transmission risks to their friends and family, reduce their chances of passing it on inadvertently, and help with getting the community back to near-normal life safely. When will the Pfizer vaccine be available? Having the AZ vaccine now is far safer than waiting for Pfizer and having three or more months completely without protection.

AstraZeneca appears to work slower than Pfizer in terms of full coverage - Is it worth taking an AstraZeneca shot in the next month if you won't get full protection for 3-4 months?

"Yes. Even one shot of AstraZeneca can bring some people up to 70 per cent protected from symptomatic COVID and one shot has an even better effect against being so sick you need a hospital admission.  Your antibody levels are rising throughout the period after vaccination and increasing your protection. It is even possible if there is an excess of vaccine in a few months that the government may permit the AZ second dose to be given from eight weeks after the first shot, so you won’t even wait 12 weeks – let’s see!

Professor Cassandra Berry

The risk of an adverse side effect of blood clotting is about 100-times higher with COVID-19 than the normal population, not exposed to the virus. As only five per cent of Australians are fully vaccinated we are in a precarious position.  The highly transmissible Delta variant imposes a greater danger than ever before during the pandemic."

Should young people be getting the AstraZeneca vaccine or wait for the Pfizer?

All people in Australia with accessibility to the current approved AZ COVID-19 vaccines should consider vaccination at their earliest convenience. We do not have the luxury of waiting too long for imported Pifzer, Moderna or Novavax vaccine supplies to arrive.

AstraZeneca appears to work slower than Pfizer in terms of full coverage - Is it worth taking an AstraZeneca shot in the next month if you won't get full protection for 3-4 months?

"Yes, people should go ahead and book their AZ jab. New clinical trial data from Oxford showed better anti-viral immune responses (B and Th1 type cells) with good safety for AZ first shot and Pfizer BNT second shot. The levels of immunity suggests efficacy at preventing symptomatic COVID-19 and hospitalisations.

This heterologous [mixed] vaccination strategy uses different vaccines types and has already been tested for other viruses: influenza, ebola and dengue. It is designed to focus the attention of the immune response on the common viral spike without being distracted by the vaccine backbone components. The anti-viral immune response is robust, potent and more durable than using homologous vaccination regimen using single vaccine types. More studies are continuing for mixing vaccines for COVID-19."

Are there any additional comments you would like to make about the COVID situation and Australia’s COVID vaccines?

"Given a flexible approach, taking AZ as first dose followed by Pfizer as second dose, after just a short interval of 28 days instead of waiting 12 weeks will speed up vaccination coverage and fast track protective immunity in our country.

The government should consider this as a gamechanger and review the guidelines in light of the Oxford Com-COV study. This approach would utilise our vaccine supplies, accelerate vaccine roll out, provide immunity to protect our vulnerable. It is also especially vital to assist our low income neighbouring countries.

Dose-sparing may be an answer to solve the problem of lack of vaccine resources currently in Australia.

A rationing approach was used in the 1918 Spanish flu pandemic with shortages of vaccines for populations.

Lower doses (LD fractions) than the standard dose (SD) were used to vaccinate those requiring protection rather than leaving them unimmunised.

This is currently being investigated at University of Rochester, US, with promising results. Researchers observed better memory B cells responses in a LD/SD regimen with higher levels of antibodies in a mouse study. Vaccine fractionation is perhaps another strategy to extend vaccine supplies to meet demands of protecting people against COVID-19 instead of having them wait anxiously for months during lockdowns.

Professor Adrian Esterman

Why is the AMA disagreeing with Scott Morrison’s decision to make the AstraZeneca vaccine available to under-40s?

"I think that they are fed up with the government’s constantly changing criteria and poor messaging."  

Should young people be getting the AstraZeneca vaccine or wait for Pfizer?

"Given the current situation in Australia with multiple outbreaks of the Delta variant, the answer is yes – however, there has to be informed consent about the risks."

How does the risk of dying from AstraZeneca jab compare with risk of dying from COVID in different age groups?

"The European Medicines Agency, provide data on deaths from COVID-19 for every 100,000 people, and the number of cases of the rare blood clots for every 100,000 people after a single dose of AstraZeneca. If we assume that one in five of those with blood clots die from this condition (which is now probably very conservative), the benefit of the vaccine outweighs the risk of blood clots at all age groups above 20-29."

How does the risk profile of AstraZeneca compare with Pfizer and Novavax (which is a vaccine we will get later in the year)?

"There are serious side effects for the Pfizer vaccine, including anaphylactic shock, myocarditis and pericarditis. However, these are rare and treatable.  There have been a few reports of serious adverse events coming from a Phase 3 clinical trial of Novavax, but there is the same incidence in both the placebo and vaccine arms of the trial."

AstraZeneca appears to work slower than Pfizer in terms of full coverage - Is it worth taking an AstraZeneca shot in the next month if you won't get full protection for 3-4 months?

"The UK has already reduced the timing from the first to second dose of AstraZeneca for those with a higher risk profile from 12 weeks to eight weeks. I would like to see that introduced in Australia.

Professor Fiona Russell

AstraZeneca vaccine is a highly effective vaccine.

Any adult should be able to get access to this potentially life-saving vaccine provided informed consent is given on risks and benefits.

AstraZeneca and Pfizer vaccines are equally effective for all the outcomes tested against Alpha and Delta variants.

Delta vaccine effectiveness results from UK:


For hospitalisations:

After one dose of AZ: 71% effective; and after two doses, 92% effective

After one dose Pfizer: 94% effective and after two doses, 96% effective

For symptomatic infection:

after one dose AZ: 33% effective and after two doses, 60% effective

after one dose Pfizer: 33% effective and after two doses, 88% effective

It is important to have two doses as this may prevent more infections and therefore prevent spread.

Also the protection is higher after two doses and likely to last longer based on the immune responses.

AstraZeneca vaccine has a rare, serious but treatable side effect (blood clots/bleeding) which occurs in about 1 in 35,000 people under 60 years after the first dose and 1 in 1.5 million doses after the second dose.

It occurs about 1.5-2 times per 100,000 doses in those over 60 years.

Professor Jill Carr

AstraZeneca appears to work slower than Pfizer in terms of full coverage - Is it worth taking an AstraZeneca shot in the next month if you won't get full protection for 3-4 months?

"I don’t think this is true and the rationale is based on the boosting strategy in the initial clinical trial. you don’t get full protection until 3-4 months with AstraZeneca because that is when the booster shot is recommended, not necessarily because the vaccine itself works any slower"

Are there any additional comments you would like to make about the COVID situation and Australia’s COVID vaccines?

"This is a changing situation for risk:benefit and hence I would expect our public health recommendations to continue to change and reflect that. if we get lots of COVID-19 cases in the community, then any of the vaccine candidates, that all have great efficacy, would be of benefit to prevent COVID-19 related death and overwhelming of our hospital systems.

Q&A

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