© Provided by The GuardianPhotograph: Lisa Maree Williams/Getty Images
The results from AstraZeneca's US phase 3 clinical trials for its Covid vaccine were made available this week with the vaccine showing 100% efficacy against severe or critical disease and hospitalisation. It showed 80% efficacy in those aged 65 years and over and, overall, had 79% efficacy at preventing symptomatic Covid-19.
These interim safety and efficacy results were based on 32,449 participants who had between them 141 symptomatic cases of Covid-19.
With phase 1b of Australia's vaccination rollout under way as of Monday and millions of doses of locally produced AstraZeneca vaccine due to be delivered to GP practices imminently, this is good news. Australia has secured about 10m doses of the Pfizer vaccine, but five times as many doses of the AstraZeneca vaccine will be administered, making it the predominant vaccine for Australia.
© Photograph: Lisa Maree Williams/Getty ImagesPamela Rawson speaks with nurse Emma McCallum as she receives the AstraZeneca Covid vaccine at the Sydney Road Family Medical Practice in Sydney.
So what about vaccine efficacy against variants of concern, some of which are the dominant strains circulating in other countries? And if the Pfizer or AstraZeneca vaccines show lower efficacy against these variants, what does that mean for when Australia opens its borders to those countries?
What does the science say?
A study recently published in the New England Journal of Medicine [NEJM] and funded by the Bill and Melinda Gates Foundation found a two-dose regimen of the AstraZeneca vaccine did not show much protection against mild to moderate Covid-19 due to the B1351 variant that was first identified in South Africa. Its efficacy against the variant was 10.4%. There are some important caveats to this finding, however.
It is important to remember that the primary goal of all vaccines is to protect against serious disease and hospitalisation. The NEJM study only enrolled healthy individuals less than 60 years old, with a median age of 30. In other words, this is a group unlikely to develop severe disease anyway, and in fact those in the study only developed mild disease. The trial findings are therefore inconclusive on whether the vaccine may protect against severe Covid-19 caused by infection with the variant identified in South Africa, which is the most important thing to know.
A separate, recent pre-proof paper published in Cell Host & Microbe found the Pfizer vaccine was similarly effective against the main background strain - known as the wild-type - of the virus and the variant identified in the UK. It was more than six times less effective against the variant identified in South Africa, the study found, but the sample size was small, with only 25 people.
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The executive vice-president of biopharmaceuticals research and development at AstraZeneca, Mene Pangalos, said the variant identified in the UK was now the one circulating wildly around the world and the one of most concern.
"We've shown that the vaccine has maintained very good efficacy actually reasonably comparable to what we've seen with the original Wuhan variants that were the original circulating variants," he said.
There's relatively little data about the vaccine's efficacy against the variant which originated in Brazil, Pangalos said, but pre-clinical trials seemed to show it offered similar protection as against the variant identified in the UK.
"We know all of these vaccines, including our own, do not work as effectively -particularly with these variants - against mild disease," Pangalos said.
Even if the vaccine does eventually prove to show what the NEJM study found - that it only has about 10% efficacy against mild disease caused by the variant identified in South Africa - Pangalos said: "I still think it is highly likely our vaccine will confer some protection, even against the South African variant, when it comes to more severe disease, particularly in older patients, which is ultimately the patient population we need to treat because they're the ones that end up in hospital and do most poorly if they're infected."
What does this mean for international travel?
A professor of infectious diseases at the Australian National University, Peter Collignon, has said: "In the first instance, we want to stop people dying, and getting into hospitals." Getting back to normal, and opening the border to other countries, was important but a secondary issue, he said.
Collignon argues Australia should be able to reopen so long as the vaccines prove effective against severe disease - because that's what overwhelms health systems and kills people.
"Realistically that kind of reopening is not going to happen for another year," he said.
"The reality is we're going to have to keep restrictions and some border closures going for quite a while now, whether we let people home quarantine instead of hotel quarantine or not. But we will be wiser in about four to six months' time. A lot of the restrictions will not necessarily have to be as hard as they've been in the past once we have a lot of, particularly vulnerable, people vaccinated because the consequences won't be so severe, providing the vaccines work against severe disease, which so far they do."
Has Australia's rollout been too slow to see everyone vaccinated by October as promised?
The director of infectious diseases at Mater Health Services in Queensland and a clinical microbiologist, Associate Prof Paul Griffin, said it was "clear" that Australia was not hitting the initially proposed vaccination targets.
"But it's also clear this is perhaps one of the most complex logistical undertakings that we've ever done, and we want to make sure we get this right," he said. "So we've eased into it, some would say perhaps too slowly, but I think it's really important that we ease into it steadily and get our processes right."
Griffin said "obviously" there had been some supply issues outside of Australia's control, "which is why having locally manufactured product is so critical".
"We need to just basically focus on the task at hand now. We're in a really good position and if we all focus on getting done what needs to happen I'm very confident that we'll be able to catch up."
What if other variants emerge?
All viruses continuously change. But if the spread is prolonged and not contained that provides more time and opportunity for significant changes.
The World Health Organization (WHO) says the Covid-19 vaccines that are currently in development, or which have been approved, are expected to provide at least some protection against new variants because the vaccines elicit a broad immune response involving a range of antibodies and cells.
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"Therefore, changes or mutations in the virus should not make vaccines completely ineffective," the WHO has said. "In the event that any of these vaccines prove to be less effective against one or more variants, it will be possible to change the composition of the vaccines to protect against these variants."
Pfizer is in ongoing discussions with regulatory authorities, including the US Food and Drug Administration and the European Medicines Agency, regarding a clinical study to evaluate the impact of a modified, variant-specific version of its vaccine to examine the impact on variants.
Pangalos said AstraZeneca was also working on next-generation vaccines specifically targeting variants.
"We have been now for some time since the variants arose," he said. "We aim to be starting our clinical studies, I would say, in the next few weeks. We are working very fast and very quickly to get a next-generation vaccine that will hopefully work against all of the current variants and the old variants in case we need it."
These trials are more straightforward to run given the core part of the vaccine has already been developed and proven in studies to be safe.