What's the difference between the two COVID vaccines?

As Australians navigate lockdowns, border closures, hotel quarantine and COVID-19 testing queues, the wait for the vaccines that will protect the population is slowly shortening.

But before the largest vaccination program in the country’s history can kick off next month, many of the details have to be decided, implemented and communicated to the public.

Last week, the Federal Government outlined its plan to administer the Pfizer vaccine to “first-priority groups” because Australia will get that drug first, but only in a limited supply.

Over the weekend, Chief Health Officer Paul Kelly said most Australians would receive the AstraZeneca drug as part of the Government’s strategy because “we are making it here”.

So, which are you likely to get and what’s the difference anyway?

The Pfizer vaccine

The Pfizer Biotech drug is not yet approved in Australia, but it’s likely to be the first COVID-19 vaccine to clear the Therapeutic Goods Administration’s approval process.

It has a reported efficacy of 95 per cent and Australia has 10 million doses on order.

An infosheet on the Pfizer vaccine reveals it has not been approved in Australia, 10m doses are ordered, and is 95pc effective
The Pfizer vaccine has not yet been approved for use in Australia.(ABC News)

We know the “first-priority populations” of Australians will receive the Pfizer vaccine in “phase 1a” of the rollout.

This will include:

  • 70,000 quarantine and border workers
  • 100,000 frontline healthcare workers
  • 318,000 aged care and disability care workers
  • 190,000 aged care and disability care residents

From there, the Government plans four further phases of the vaccine rollout, using the AstraZeneca drug to protect most of the population.

The AstraZeneca vaccine

The AstraZeneca vaccine was developed in partnership with Oxford University and Australia signed supply orders for the drug months ago.

The benefit of this drug is it is being manufactured in Australia by biotechnology company CSL, meaning supply is secured.

An infosheet on the vaccine reveals 53.9 million doses have been secured and the drug is 70 per cent effective.
The AstraZeneca vaccine is also yet to be approved by the TGA, but the Government has secured supply of the drug.(ABC News)

The reported efficacy is about 70 per cent and, just as with the Pfizer drug, it will be administered in two doses.

The COVID-19 vaccines will be recommended to almost all Australians and will be made available to Australian citizens, permanent residents and most visa holders for free.Catch up on the main news from January 11 with our coronavirus blog.

Why Australia will use both

Using the first-available COVID-19 vaccines that are safe makes sense, according to epidemiologist Hassan Vally.

Australian health authorities have the most comprehensive data for the Pfizer vaccine and will look at approving that one first.

“It’s important to get the vaccine out there and it makes sense to roll out the first available vaccine, the Pfizer vaccine, to vulnerable groups,” Dr Vally from La Trobe University said.

And experts said giving the AstraZeneca vaccine to the rest of the population was a good move, as it would be manufactured locally.

Dr Vally said local manufacturing put Australia in a good position.

“In terms of practicalities, it is a huge advantage to have a vaccine that we are able to manufacture onshore, given all the global issues that are likely to occur over the next 12 months,” he said.

Dr Vally said no matter which vaccine people received, the more people who got the jab, the better.

“The more people we vaccinate, the less susceptible the community is to the virus and so the less of a threat the virus poses,” he said.

Immunologist Kylie Quinn said Australia was fortunate to have two tools in its vaccine toolkit, the Pfizer jab for those most at risk and the AstraZeneca inoculation for the broader community.

“They may not be offered the more effective vaccine, but the AstraZeneca vaccine is still a pretty decent vaccine, and if we all do a good job of taking up the vaccine, then it’s going to provide that broader protection in the community,” she said.

Dr Vally said: “Every vaccination means one less person who is going to get sick.”

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The difference in how they work

Not all Australians will get the same vaccine, but both drugs are trying to achieve the same goal.

All vaccines want to train a person’s immune system to recognise a particular virus as dangerous before the person succumbs to the disease.

One way to identify the virus that causes COVID-19 is by its surface spikes, which are made of a protein unique to this virus.

To get a person’s body to recognise the virus, both the AstraZeneca and Pfizer vaccines use the body’s own cells to produce the spike protein.

They then show this protein to the body’s immune system so it can produce the cells needed to destroy any foreign organism displaying it.

Where the vaccines differ is the way they give the body’s cells the information they need to produce that protein.

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For the Pfizer vaccine, scientists have created a piece of mRNA — or messenger ribonucleic acid — that contains all the instructions a cell needs to create the protein that identifies coronavirus.

To deliver the instructions into the body’s cells, they have packaged it in a tiny fatty particle, a nano lipid.

Dr Quinn said lipids were a very efficient way of getting inside cells.

“If you’ve got a little bubble of liquid, it’s much more likely to bind to the surface of the cell and deliver its payload into the cells,” she said.

Once the mRNA is inside the cell, its machinery produces the target protein, displays it on the surface of the cell, and as a result the body’s immune system creates T-cells that now know what to look out for.

The AstraZeneca vaccine uses a weakened virus to deliver the instructions into our cells.

The scientists working on this vaccine have inserted a piece of genetic code, this time DNA, into the code of a similar virus that has been altered so it cannot cause disease.

Dr Quinn, who has worked on the development of several vaccines, said weak viruses were chosen as the carrier cells, and then they were turned into mere shells.

“We gut them further just to make sure that they really can’t cause any issues,” she said.

As with the Pfizer vaccine, when this one enters our cells, it teaches them to make the spike protein and shows it to the immune system so the T-cells know how to neutralise it when they next see it.

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