AstraZeneca vs Pfizer, and why you don’t have a choice

The second wave of the coronavirus vaccine schedule has begun, with six million Australians now eligible to be immunised.

And with the waves of media coverage on the different vaccines, people may be led to think they have a right to choose one vaccine over the other.

Unfortunately, pulling up to your local GP won’t feel like fine dining at your favourite restaurant: you won’t be handed a menu at the front desk, and the reception staff won’t take your order.

You’ll get what you’re given and for most Australians, it’ll be the AstraZeneca vaccine.

The alternative, Pfizer, has been reserved for priority groups due to limits on supply. It will mostly be used for people in the phase 1A category.

So what are the differences between them?

Storage and time between shots

Major differences between the vaccines lie within storage capabilities, and the time needed between booster injections.

Both are two-shot vaccines, but Pfizer doses are spaced three weeks apart, whereas AstraZeneca doses are spaced almost four times that length, at 12 weeks apart.

USC clinical research investigator Peter de Wet says AstraZeneca’s waiting period was less practical than Pfizer’s.

“It’s unfortunate, because that’s quite a delayed vaccination program, and you haven’t achieved full immunity until that second dose is given,” he said.

Although AstraZeneca takes longer to achieve full immunity, it makes up for it in its durability.

AstraZeneca can be kept at room temperature for nearly six hours, and only requires standard refrigeration for storage.

Pfizer, however, must be cooled to temperatures below -70℃, and only lasts at room temperature for short periods.

Dr de Wet says the difference in storage-needs makes Pfizer difficult to distribute. He says very few general practices and small health hubs will have the cooling equipment needed to house the vaccine.

Dr de Wet says AstraZeneca is more widely used for that reason.

“From a practical point of view, for the people administering and keeping these [AstraZeneca] vaccines, that’s a huge benefit, but to the patients receiving it, the three-month wait is a bit of a pain,” he says.

Australia’s next coronavirus vaccine


In a US scientific trial, Pfizer found its vaccine was 95 per cent effective in stopping symptomatic cases.

In a new US clinical trial, AstraZeneca showed to be inferior in efficacy, as it was 79 per cent effective in stopping symptomatic cases.

Dr de Wet says people with severe health risks should ideally be given Pfizer due to the higher rate in effectiveness.

“From an individual perspective, you want the one that has the higher assurance, of the efficacy, so you can feel more safe and comfortable when you’ve had the vaccine. Ideally, the Pfizer should be given for that reason,” he says.

Despite this, he says the Federal Government’s plan to immunise most Australians with AstraZeneca should lead to herd immunity.

“From a population health point of view, if enough people were vaccinated, it probably doesn’t matter if we can get 80 per cent vaccination of the population from both doses of the AstraZeneca, even though it’s only 79 per cent effective. That should still give us protection.”

Side effects

Dr de Wet says both vaccines had the risk of similar side effects, including flu-like symptoms that cause fever, headaches and muscle pain.

However, he says this only occurs around 10 per cent of people.

But what about blood clots?

There have been reports of some patients forming blood clots after receiving the AstraZeneca vaccine.

Government officials in Munich and Berlin even went as far to ban the vaccine for people over 60, after the country’s medical regulator says they had 31 reports of blood clots in patients who have been administered AstraZeneca.

Dr de Wet says several investigations have disproved correlation between blood clots and patients taking AstraZeneca.

These investigations include one from the European Medicines Agency, who has concluded the vaccine does not increase general threat of blood-clotting.

The review cites less than 30 cases of severe blood clots among 20 million people who have been administered AstraZeneca.

As the Phase 1B vaccination rolls out, Frazer Ramsden headed out to interview Sunshine Coast citizens in an effort to understand public sentiment about the jab.

Adenovirus-vectored technology vs mRNA.

AstraZeneca uses technology that trips up your tongue as well as it trips up your immune system: adenovirus-vectored technology.

It’s essentially a common cold infection that has been altered to extract harmful properties that will make people sick. The virus contains a gene from COVID-19’s spike protein, and once in the human body, activates people’s immune system to develop anti-bodies and protect cells against coronavirus.

Or, in layman’s terms, and as AstraZeneca put it, the vaccine replicates and infects you with coronavirus but without life-threatening effects.

Pfizer, on the other hand, uses technology that’s much easier to say, but less tested and trialled – mRNA.

Pfizer is the first company to create a vaccine with this technology. This has created excitement, bewilderment and concern in the medical world.

mRNA injects a piece of genetic code into your body to create a similar spike protein that AstraZeneca uses to fight off COVID-19. Both vaccines are comparable in their protection process, but one uses a modified version of a virus, whereas the other uses viral DNA.

Dr de Wet says the technology AstraZeneca uses has been clinically trialled and researched vigorously, suggesting it’s a safe option for vaccine creation.

He says despite mRNA being a new method for vaccine creation, it’s secure and practical.

“I was a little apprehensive, or sceptical, because of the new technology, but it’s only a new technology to vaccines,” he says.

“The technology has been researched and perfected for lots of other therapeutic reasons aside from vaccines, not just vaccinating other viral illness, but also treating medical disorders with genetic therapy straight to the cells, so I think it’s going to have a lot of implications for drug delivery in general.

“I’m comfortable that the safety data that’s come through [for mRNA technology] has been excellent, and I don’t think there needs to be any concerns, although it sounds very sci-fi.”

Should Australians have a choice?

Supply and demand are like opposite sides of a magnet in the case for Australia’s vaccine rollout, forcing many phase 1B qualifiers to settle for the less effective but more accessible AstraZeneca injection.

Practicality and efficacy are the main concerns for high-risk people that can’t get their hands on Pfizer, as the vaccine has shown to be 10 per cent more effective at preventing symptomatic cases and has nine less weeks of waiting time in-between shots.

These points beg the question – should Aussies have a choice over which dose they’ll receive?

“In an ideal world, yes,” Dr de Wet says. “There’s a lot of information about these different vaccines, and they’ve been widely publicised in media. Therefore, more people are educated, which is always a good thing.

“Based on that, they’re going to develop preferences on the information available.

“Again, it comes down to supply, and if we can’t guarantee one vaccine for everyone in the country, then we can’t allow everyone to refuse another treatment for hopes they can wait for one that they prefer.

“In the interest of getting the vaccine into as many people as possible, we have to accept that some people will not get their preferred treatment.”