Monday, October 25, 2021

Australia’s chief medical officer defends AstraZeneca’s Covid vaccine amid efficacy concerns

Australia’s chief medical officer Professor Paul Kelly and infectious diseases experts have defended securing 54m doses of a Covid-19 vaccine made by Oxford University and pharmaceutical company AstraZeneca, amid concerns the vaccine will not be effective enough to achieve herd immunity.

The president of the Australian and New Zealand Society for Immunology, Prof Stephen Turner, told Nine media that Australia should halt the AstraZeneca vaccine rollout because it has “lower efficacy”.

“You cannot rely on it to establish herd immunity,” he said.

The head of the Western Australian branch of the Australian Medical Association, Dr Andrew Miller, who is an anaesthetist, echoed the comments to the Australian, saying: “We need to pause and look at what the outcomes are going to be before we take any further steps.”

Interim results of the Oxford/AstraZeneca Covid-19 vaccine trials found that the vaccine protects against symptomatic disease in 70% of cases, with vaccine efficacy at 62% for those given two full doses, and 90% in those given a half then a full dose.

Kelly said on Wednesday the AstraZeneca vaccine is effective, safe and high quality.

“But those are the things that the TGA [Therapeutic Goods Administration] will be looking at with their full approval coming very soon … and we’ll be guided by their assessment of the vaccine,” he told the ABC. He said Australia had also secured doses of other vaccine candidates, including the Pfizer vaccine.

The Pfizer vaccine is a new kind of vaccine, containing strands of genetic material called mRNA. When this enters cells in the body, it instructs them to make a piece of the “spike” protein that is unique to the virus. Those harmless protein pieces trigger an immune system response so if infected with the real virus, the body will know how to attack.

The Oxford University/AstraZeneca vaccine is a viral vector vaccine, containing a weak or inactivated virus that cannot cause disease. This virus has genetic material from the Covid-19 virus inserted in it. Once the viral vector is inside human cells, the cells make a protein unique to the Covid-19 virus. This triggers the body to begin to build an immune response.

One of the benefits of the AstraZeneca vaccine is that it can be manufactured in Australia, whereas the technology for mass production and cold-chain storage of the newer mRNA vaccines is not available in Australia. Fifty-one million doses of the Novax protein vaccine have also been secured, and Australia has joined the Covax Facility, which will allow more vaccine doses and other vaccines to be purchased as they become available.

“We have several eggs in the basket,” Kelly said, adding that the US, UK and others had also secured millions of doses of the AstraZeneca vaccine.

Prof Lyn Gilbert, the chair of the Infection Control Expert Group, which provides independent and evidence-based advice to the federal government, said comments calling for the AstraZeneca vaccine rollout to be halted were “misguided”.

“It is based on too little information about efficacy and duration of protection, or the ability of any of the vaccines to prevent transmission; an assumption that there will be unlimited availability of what are seen to be the most efficacious vaccines which are currently mRNA vaccines such as the Pfizer vaccine, for everyone; and an unrealistic expectation that elimination of the virus is possible,” Gilbert said.

Professor of infectious diseases and former World Health Organization advisor, Peter Collignon, described calls to halt the AstraZeneca delivery as “mania”.

“If you look at Melbourne, if all those people in nursing homes had been vaccinated with that AstraZeneca vaccine before that second wave, that would have saved about two-thirds of the deaths,” he said. “It’s not not perfect, I’d love to have 90% or 100% efficacy. But with the first lot of vaccines you may not get the dose schedule optimally organised all the time, and that will be seen after it’s rolled out more widely.”

He said some of the people calling for it to be halted were the same people or groups “who were saying three weeks ago, ‘Don’t hold up the rollout in Australia, just roll it out now.’ I think this has gone from one extreme to the other.”

Meanwhile the federal Australian Medical Association president Dr Omar Khorshid distanced himself from the comments made by his WA counterpart. Khorshid said while the government could invest in other types of vaccines in addition to the three already secured, it was too early to know whether any of the vaccines would stop virus transmission as well as severe disease.

“The government did deals with a number of companies well before there was any data about whether their vaccines were ever going to come to pass,” he said.

“And so far, two of those look like they’re going to be available in Australia, and there’s potentially more to come. And we don’t know which vaccine’s going to be best for which different parts of the population, and that’s all data that we’re going to find out more about as time comes.”

The co-chair of the Australian Technical Advisory Group on Immunisation, Prof Allen Cheng, said it was important to remember that the AstraZeneca vaccine has not yet been registered by Australia’s drugs regulator, the Therapeutic Goods Administration. Neither has the Pfizer vaccine.

“I think that we’re in the fortunate position where we can be cautious,” he said.
“Australia currently has access to 10m doses of the Pfizer vaccine to be delivered over a year, and 53m doses of the AstraZeneca vaccine to be delivered at roughly one million doses a week. We don’t know to what degree these reduce transmission. The AstraZeneca vaccine didn’t reduce asymptomatic infection, and this hasn’t been looked at in the Pfizer vaccine study.

“Even if the Pfizer vaccine was fully effective against transmission, covering 20% of the population over a year would be unlikely to achieve herd immunity. So the choice we have is not whether to use one or the other, it is whether to use what we have – I’d think that there is a benefit in getting protected against disease, even if it doesn’t reduce transmission to the degree that we would like.”

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