Extract from ABC News
By the Specialist Reporting Team's Penny Timms, Leonie Thorne, and national medical reporter Sophie Scott
Back in April, the Prime Minister stood up at a late-night press conference and announced the Pfizer vaccine would be preferred over AstraZeneca for most people under 50.
Key points:
- Two doses of AstraZeneca is 92 per cent effective against hospitalisation from the Delta variant, a UK study found
- Another pre-print study has found even just one dose is effective against hospitalisation and death
- One expert said success wouldn't be about eliminating COVID, but reducing its harmful impact
The advice has changed a few times since then, and now everyone over the age of 18 in Greater Sydney is being encouraged to get vaccinated with any available vaccine, including AstraZeneca, to help bring the current outbreak under control.
But even though demand for the vaccine has "gone through the roof" in recent days, according to NSW Premier Gladys Berejiklian, many people are still hesitant about AstraZeneca.
With months of changing advice and reports about extremely rare cases of the blood clotting condition TTS, it's easy to see why confidence in the vaccine plummeted.
But if you're still on the fence about whether or not to get the vaccine, here is what the latest data says.
AstraZeneca does protect against severe illness and death from Delta
The initial trials of various COVID-19 vaccines were large, but they took place before the Delta variant had emerged.
Now that millions of people globally have been vaccinated, we have learned about how AstraZeneca's jab performs in a world where Delta is the predominant strain, Nick Wood from the National Centre for Immunisation Research and Surveillance said.
"What we know now is that … two doses of the AstraZeneca or the Pfizer vaccine will give you very good protection against the severe disease, like hospitalisation or even death," Dr Wood said.
"Even a single dose would give you some good protection against the Delta strain."
This understanding of how the vaccines perform is mostly based on data that has recently come from the UK and Canada.
Two doses of the AstraZeneca vaccine was about 92 per cent effective against hospitalisation from the Delta variant, a Public Health England analysis of about 14,000 cases found.
That's comparable with the 96 per cent effectiveness against hospitalisation offered by the Pfizer jab.
A recent study from Canada, which is yet to be peer-reviewed, found even just one dose of AstraZeneca's vaccine was about 88 per cent effective against hospitalisation or death from the Delta variant.
Comparing vaccines can be difficult because each outbreak is unique and variants are still emerging.
That means data about each vaccine's efficacy is also changing, epidemiologist Nancy Baxter says — but the evidence on the AstraZeneca jab is promising.
"The key thing is that we want this vaccine to stop you getting hospitalised or dying, and one dose of either vaccine really does give you a very good protection against that severe outcome," she said.
AstraZeneca's jab does help reduce the risk of transmission
Neither the AstraZeneca nor Pfizer vaccines totally eliminated the risk of catching COVID, passing it on, or developing mild illness — but they do reduce the risk, Professor Baxter said.
The current situation in England is a good example of this. Cases have gone up, even among people who have been vaccinated, but hospitalisation rates are nowhere near the levels seen pre-vaccination.
That's also a point made by Tony Kelleher, a clinician scientist and director of the medical research organisation The Kirby Institute.
He said while AstraZeneca's jab was not as effective as other vaccines, like Pfizer, when it came to a person's chance of contracting the illness, AstraZeneca was always known to be good at preventing severe illness from COVID-19.
"If you define its efficacy
against preventing people getting sick enough to go to hospital, it is
as effective as any of the other vaccines," Professor Kelleher said.
Why were there reports of AstraZeneca's jab being 'less effective'?
There are different ways of measuring vaccine effectiveness. Some measures involve looking at your immune system's response, while others involve measuring the rate at which people who are vaccinated get sick, go to hospital, or die.
Professor Baxter pointed out a lot of that initial understanding of AstraZeneca and its efficacy related to how it responded to the original strain of COVID-19 and preventing any infection.
That all changed when the Delta variant came along.
At our current pace of roughly 1,140,671 doses a week, we can expect to reach the 40 million doses needed to fully vaccinate Australia’s adult population in mid January 2022.
"When we were thinking that we could kind of block transmission — so block anyone from getting COVID and passing it on — then I think there was this narrative that Pfizer was the preferred vaccine," she said.
"Now Delta's kind of changed that equation because what we've seen in other countries is that Pfizer [and] all of the vaccines seem to be less effective in terms of preventing any infection."
With so much of the world yet to be vaccinated, Professor Kelleher said success would no longer be about eliminating COVID-19 but reducing its harmful impact.
"If we can change this into the common cold … then that's a real win, right?" he said.
"If the worst that anyone gets is [having] a couple of days off work, I think that's golden."
The recommendations are based on risk by age
The reason Pfizer was the preferred vaccine for people under 60 was because the risk of developing TTS after an AstraZeneca vaccine in that age group was higher than for older age groups.
The Australian Technical Advisory Group on Immunisation (ATAGI), the group of experts that gives the government advice on vaccines, decided the benefits of AstraZeneca outweighed the rare risks in older age groups.
For people under 60, the estimated risk is about 2.6 in 100,000, and for older people it is roughly 1.7 in 100,000, a recent update from ATAGI said.
But the risk of having severe outcomes from COVID climbs steeply as you age.
Compared with 18-29-year-olds, the risk of dying from COVID is 35 times higher in 50 to 64-year-olds, 95 times higher in 65 to 75-year-olds, and 600 times higher in those who are 85 years and older, a dataset from the United States' national public health agency showed.
In Greater Sydney, the growing likelihood of catching COVID has changed the risk-benefit equation, and that's why everyone is being urged to consider getting vaccinated with AstraZeneca, even if they're under 60.
A recent pre-print study from Europe that looked at data from more than 1 million people vaccinated against COVID in Spain found the risk of blood clots after getting COVID was higher than the risk of getting them after AstraZeneca's vaccine.
But if you're worried, talk to your GP
Thousands of people under 60 have had the AstraZeneca jab already, citing a desire to get vaccinated as soon as possible with whatever they can get access to, rather than waiting for Pfizer.
But there are also many people who are hesitant.
In a recent ABS survey, an estimated 35 per cent of unvaccinated people aged 50-69 said wanting a different vaccine was a factor in their decision not to get vaccinated.
It's important to talk to a doctor if you have any concerns about the vaccine or your personal situation.
But Professor Kelleher said data showed AstraZeneca was just as good as other vaccines when it came to what mattered most — preventing hospitalisation and severe disease.
"After all, that's what this is all about," he said.
"We want to stop people getting sick. We want to stop them dying. We don't want them suffering the morbidities that are associated with going to ICU and we don't want these people clogging up and overwhelming the hospital system.
"So that, to me personally, is the gold standard measure of efficacy."
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