How important are COVID vaccine efficacy rates?

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Covid 19 Vaccine Bottles

Experts weigh in on whether greater investment in candidates with a higher efficacy rate would actually provide the greater promise of elimination.
The spotlight is on AstraZeneca’s candidate, co-developed with the University of Oxford, as Australia moves closer to its mid-February vaccine rollout.

As the US, UK, and Europe continue to record thousands of daily new cases of COVID-19, it has been said time and again that Australia is in an enviable position.

The vaccine roadmap is expected to begin with 10 million doses of Pfizer’s mRNA vaccine. But as the rollout date inches closer, concerns have been raised over the Federal Government’s decision to secure and manufacture 53.8 million doses of AstraZeneca’s vaccine.

Co-developed by the University of Oxford, preliminary data shows the vaccine is around 70% effective compared to Pfizer and Moderna’s mRNA vaccines that have shown  95% and 94% efficacy, respectively.

‘We really don’t have enough information to know where it will ultimately fall,’ Professor Godfrey said.

‘There are more trials underway, and it’s only through those updated trials that we’ll have a much better idea about the actual efficacy of the AstraZeneca vaccine.

‘It’s also possible that we could start with one vaccine, which gets us on the path towards protection, and then get a boost from a different vaccine down the track when let’s say six months or a year from now maybe the Pfizer vaccine or another vaccine is more widely available.’

Aside from efficacy, Professor Godfrey notes that there are a number of other factors to consider in a pandemic environment – starting with accessibility.

‘I gather that we have the AstraZeneca vaccine as the most readily available one for us at the moment,’ he said.

‘If [Pfizer] was [available] in unlimited amounts, then presumably everyone in the UK and other countries in the world with high infection rates would be getting fully immunized now, and that’s obviously not happening – instead, they are trying to find ways to spread limited amounts of vaccine as far as possible.

‘So it is unclear whether Australia could access 50 million doses of the Pfizer vaccine now, even if we decided to.’

Epidemiologist Professor Raina MacIntyre says Australia should scrap its deal with CSL and invest in more doses of a vaccine with a higher efficacy rate.

When it comes to cost, AstraZeneca’s vaccine is also undoubtedly more cost-effective in the short term.

Set to be manufactured in Australia, it comes in at about US$2.50 (AU$3.25) per dose compared to Pfizer at US$20 (AU$26) and Moderna between US$15–25 (AU$19.50–32.20) per dose, with an additional outlay for cold chain infrastructure.

Logistically that also makes AstraZeneca more desirable, as it can be stored and transported at 4°C, while Pfizer must be transported at –70°C making it ‘tricky’ for regional and rural parts of the country, Professor Godfrey says.

But Professor Macintyre says Australia should be thinking long-term by investing more now and drawing on the skilled GP workforce as much as possible.

‘One option would be to actually invest in the cold chain infrastructure, and maybe large GP practices [can] put their hands up to say “we can do this” and invest in providing them freezers,’ she said.

‘Or, get the Moderna vaccine … because that can be refrigerated.

‘We’ll have less burden on the health system [and] less ongoing headaches [long-term].’

Given the many unknowns that remain, however, Professor Godfrey says it is hard to be definitive about what will constitute as more cost-effective.

‘Costs will in part be reflected by how many people end up in the hospital, or worse, in ICU. Those are massive costs,’ he said.

‘So any vaccine that stops that from happening could be considered as cost-effective, and not to mention the effect that it will have on confidence in the community.

‘The AstraZeneca vaccine protected 100% against severe COVID. So if the priority is to stop people from going to the hospital and dying from COVID, the AstraZeneca vaccine looks like it will do that. That’s something that six months ago, we’d say “yes, that’s fantastic, give us this vaccine”.’

An AstraZeneca spokeswoman recently told the Sydney Morning Herald the company expects to deliver updated data to the Therapeutic Goods Administration this month.

But even though the full data has not been released and the AstraZeneca candidate has a number of demonstrable advantages over other COVID vaccines that have been approved for use, Professor MacIntyre is clear in her stance; Australia is at a crucial point in the pandemic timeline.

‘It’s like a fork in the road – whichever choice we make will take us one way or another,’ she said. ‘Either into a situation where we’re living with COVID forever, or a situation in which we can actually achieve elimination of COVID in Australia.’

However, Federal Health Minister Greg Hunt defended the selection of the AstraZeneca candidate and rejected claims that it would prevent Australia from reaching herd immunity and eliminating the virus during a press conference on Tuesday with RACGP President Dr. Karen Price.

‘We’re listening to the Australian Government medical experts … And they’ve chosen [other candidates] on the basis that an mRNA vaccine has never ever been done before – for anything,’ he said.

‘The advice again, and I spoke with the Chief Medical Officer only last night, is that this is what the medical expert panel of Australia … has recommended and of all the different things on which to follow the advice of medical experts, the choice of vaccines is probably the most important.

‘I think it’s absolutely fundamental, that we follow the advice of the group that every year, helps identify the flu [and] that helps identify the childhood vaccinations that keep us safe.’

While Professor Godfrey agrees that a candidate like Pfizer currently appears likely to make the path towards elimination ‘easier and more rapid’, he says it is not as clear-cut as it has been made out to be.

‘There are so many unknowns, and that’s the problem with COVID,’ he said.

‘We still don’t know how the Pfizer vaccine is going to perform long-term. It’s [also] unclear whether [it] will provide what we call sterilizing immunity. We know it stops COVID disease, but we don’t know that it stops infection and transmission.

‘If it doesn’t stop infection and transmission, then it also may not guarantee that we can reach elimination. We will just keep learning as these vaccines are rolled out.

‘We still have to keep assessing the data, making sure we’re on the best path we can be on, while the data is still unfolding. Regularly reassessing the evidence is the way, I think, it’s best handled.’

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