More than 410,000 doses of the AstraZeneca and Pfizer Covid-19 vaccines have been administered throughout Australia.

The rollout is set to ramp up rapidly now that locally produced AstraZeneca doses have been approved for distribution by the Therapeutic Goods Administration.

But will Australia need more than that to ensure all adults get vaccinated and stay protected in the long term? And what are the other vaccines on the market?

Guardian Australia spoke to Prof Jim Buttery, a paediatric infectious diseases physician and clinical researcher. He is a member of the Advisory Committee on Vaccines, which provides independent medical and scientific advice to the health minister, Greg Hunt, and the TGA.

How does the Johnson & Johnson vaccine rate?

One option to bolster Australia’s supply is the one-dose Johnson & Johnson vaccine.

“The Johnson & Johnson vaccine is different in that it’s a single-dose vaccine,” Buttery said. “So for some people that may be particularly attractive. It’s been shown to be effective in clinical trials against symptomatic disease, with about 66% efficacy, and this is much higher again [85% protection] against severe disease.”

In clinical studies, the Johnson & Johnson vaccine was effective against variants of the virus first identified in South Africa and the UK, but these variants were not circulating widely when larger clinical trials for the Pfizer and AstraZeneca vaccines began.

The Johnson & Johnson vaccine was authorised for emergency use in the US in February.

It is similar to the AstraZeneca vaccine in that it is a viral-vector vaccine that uses a harmless virus – not a coronavirus – to trick cells into making the spike protein of the Covid-19 virus. This spike is on its own a harmless part of the virus, but the body recognises this spike shouldn’t be on our cells and begins to build an immune response. It means if we do become infected with Covid-19, the immune system recognises the spike protein and fights the virus.

But where the Johnson & Johnson vaccine is unique, is in the virus it uses as a vector – a non-infectious virus called adenovirus 26. This virus carries unique genetic information, or DNA, from the Covid-19 virus and uses that genetic information to produce the spike protein on the cell’s surface. This triggers a strong immune response, though like other Covid-19 vaccines, it is unclear how long this response lasts.

According to Buttery: “You can roughly divide the vaccines into two groups: ones that trick the human body into making the Covid spike protein, which is a bit of a virus that protection forms against – and that’s the RNA vaccines and the adenovirus vector vaccines.”

The other category of vaccines deliver the spike protein into the body as part of the vaccine and our immune system reacts against that, Buttery said. This is the category of vaccine Novavax falls into.

What about the Novavax vaccine?

The TGA issued a provisional determination for this vaccine in January, and the government has entered into a contract to secure 51m doses should the TGA approve it. Like the Johnson & Johnson vaccine, the clinical trials for Novavax took place later, so it means people with more infectious variants of Covid-19 were captured in the data.

The results are promising. Interim results from phase 3 clinical trials suggest the vaccine has 95.6% efficacy against Covid-19, and it shows more than 85% efficacy against the variant identified in the UK. This is the most likely vaccine to be approved next in Australia.

When will they be available in Australia?

The federal government has said Novavax will be available in Australia in the first half of 2021 if all the approvals are given. It has not given a timeline for the Johnson & Johnson vaccine if it is approved, and unlike the Novavax vaccine, no contract has been signed to secure it.

However, even if these vaccines are approved, they will need to be imported, with the AstraZeneca the only vaccine Australia is producing locally. As seen with the AstraZeneca vaccine before locally produced doses were available, these imports can be vulnerable to supply chain and political issues.

Where is the approval process up to?

As well as the Pfizer and AstraZeneca vaccines, the one-dose Johnson & Johnson Covid-19 vaccine and the Novavax two-dose vaccine have been granted a provisional determination by the TGA. Unlike the Pfizer and AstraZeneca vaccines, the latter two have not been granted provisional approval.

A provisional determination means the manufacturers are now able to submit preliminary clinical data, and evidence of a plan to submit more comprehensive clinical data down the track. Both Novavax and Johnson & Johnson have done so.

A formal evaluation is now being carried out in multiple stages by the TGA and independent technical experts, including the Advisory Committee on Vaccines. This process is required before any decision can be made about whether the vaccines are granted provisional approval.

Provisional approval is only given to medicines that provide a promising treatment for a serious or life-threatening condition. This makes the medicine available for a limited period for those who desperately need it while the pharmaceutical company completes final clinical trials. Usually, drugs are not available until after all clinical trials have been completed.

As a condition of provisional approval, the drug companies must still commit to finish their clinical trials and submit all of their data for review. If they don’t, the TGA can cancel the approval. When the provisional approval period ends, the full evidence is reviewed and if the benefit of the medicine outweighs the risks, it’s given full, ongoing approval.

No Covid-19 vaccine has been given full ongoing approval by the TGA yet, because the final data from phase 3 clinical trials is still being collected and reviewed, but enough data was analysed before the available vaccines in Australia were approved to show they are safe and effective. Phase 3 trials usually involve thousands of participants and are scientifically rigorous.

It is important to note that provisional approval is different to the emergency approvals given to vaccines by the US, where the vaccines were rolled out in the absence of the amount of data Australia was able to wait for, since the situation in Australia was less urgent. “The TGA has not licensed any vaccine to date that does not have phase 3 clinical trial information,” Buttery said.

What about other vaccines being issued globally?

“The Australian government has signed contracts to more than cover the Australian population, so it’s unlikely that Australia would seek further contracts with Moderna or other suppliers, unless there was a problem with supply,” Buttery said.

It is important to note that while there has been much discussion about the efficacy of the various vaccines, all of them, from AstraZeneca to Moderna, show high efficacy against serious disease and death. Buttery said Australia was in a fortunate position to already have the AstraZeneca and Pfizer vaccines available at a time when there was no virus circulating in the community.

And the federal government insists there are no supply issues, with Hunt saying that between the Pfizer and AstraZeneca vaccines alone, Australia has enough supply to vaccinate all eligible Australians “three times over”.

This content first appear on the guardian

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