The Pfizer/BioNTech COVID-19 vaccine has been granted provisional approval for use in Australia by the Therapeutic Goods Administration.
The regulator said on Monday that after an independent review, the vaccine had met high safety standards.
The vaccine has been approved for people 16 years and older, with two doses required at least three weeks apart.
The federal government said the first vaccines were expected to be administered in late February, a slight delay on earlier predictions of mid-February.
Assurances despite 'supply shock' and delays
If there are delays, the vaccine could be rolled out in March, but the government has stressed advice from Pfizer that a February rollout was likely.
A final date has yet to be confirmed due to production delays at the vaccine's European manufacturing plant as it ramps up production on the vaccine.
Despite the delays in production, Prime Minister Scott Morrison said "no Australian vaccines - i.e. vaccines destined for Australia - have been diverted anywhere else".
Health Minister Greg Hunt said he had spoken with representatives of Pfizer, who had assured him they would be able to ship the first doses of the vaccine, of which Australia has ordered 10 million, in time to start vaccinating in February.
"Those shipping times were provided last night, which means we are in a position to commence in late February and our guidance has always been for a window," Mr Hunt said.
"I would say that has undoubtedly been influenced by Pfizer's global capacity and the fact that we are within our window is indicative of a very strong contract and a very strong position."
Australia will also be affected by production delays of the AstraZeneca vaccine overseas, with the early doses to come later than first planned.
Yet to be approved in Australia, the AstraZeneca rollout will include a small number of initial imported doses, with the bulk to be manufactured in Australia.
The delay means Australia is unlikely to meet its goal of administering 4 million doses by the end of March, with that target moved to early April.
"The one variable here is AstraZeneca globally advised us yesterday that, as we have seen, they have had a significant supply shock and so that means we won't have as much of that AstraZeneca international in March as they had previously promised," Mr Hunt said.
The delays in production overseas vindicated the government's decision to pay "a premium" and invest in onshore manufacturing capacity at CSL's facility in Melbourne, Mr Hunt said.
'Best guess' on vaccine safety for pregnant women
Unlike in many other countries, Australia's regulator has not used emergency processes to approve the Pfizer vaccine for use, instead using a prioritised provisional determination process.
There were fears the approval process could be delayed after Norway reported a number of deaths in elderly and frail aged care residents after receiving the vaccine.
Despite this, the Therapeutic Goods Administration has not yet released specific advice on whether the vaccine is approved for the very elderly or terminally ill.
That decision will be left to doctors to decide if their patients should receive the vaccine.
"The TGA advice - and we have been concerned about this - for the very elderly and frail, that will need a very careful clinical decision," Health Secretary Brendan Murphy said on Monday.
"That is something that would need to be, where the risks versus the benefits of vaccination need to be carefully considered."
Professor Murphy said although the vaccine was registered for use for all people older than 16, the Australian Technical Advisory Group on Immunisation would produce specific advice for different groups, including people who were frail and close to the end of their lives.
There is also no clear answer yet on whether pregnant women should get the Pfizer vaccine, as pregnant women weren't included in clinical trials, meaning there is no data on safety for women or their babies.
"Theoretically the risk of this vaccine, Pfizer or AstraZeneca, on pregnancy is probably very low," Professor Murphy said.
In the United Kingdom, pregnant women are being told not to get the Pfizer vaccine, while in the United States pregnant women are told it is a personal choice.
"We will be getting advice from [the Australian Technical Advisory Group on Immunisation] and it is advice that is just going to be based on the best guess of what the risks are at the moment and that is coming very shortly, before the vaccine is administered.
Managing supply for rollout
Manufacturing and logistical issues have plagued other countries' vaccine rollouts, and Australian authorities are banking on local capacity to manufacture the AstraZeneca vaccine to avoid such problems.
The first Australians to be vaccinated will receive the Pfizer jab though, and the Australian government also faces the challenge of ensuring there is enough supply to make sure each person gets their first and second injections at the right times.
"Because we have got the luxury of doing this properly, we plan to make sure that we have enough vaccine to give everyone the second dose at the recommended time," Professor Murphy said.
While in the United Kingdom, the period between the first and second vaccine has been stretched out to allow more people to receive their first dose more quickly, this won't happen in Australia.
"We are not planning to manipulate the revaccination times. We are doing our planning on the basis we can give people the recommended doses at the recommended intervals."
While not providing details, Mr Morrison assured reporters supply issues wouldn't affect people getting their second dose at the right time.
"You don't start what you can't finish, and finishing the job involves two doses," he said.
Mr Morrison said the digital system that will be in place for the vaccination rollout will ensure people get their second dose at the right time, and that they go to the same location to complete their doses.
Who will get it first?
A priority group of Australians are expected to receive the first doses of the vaccine as soon it arrives in the country.
Group 1A for the vaccine rollout includes quarantine and border workers, frontline healthcare workers, aged-care staff, aged-care residents and disability care staff and residents.
It's estimated up to 1.4 million doses will be required for the first stage of the vaccine rollout.
Within that first group, it is not clear yet who will be first.
"The Department of Health is making sure that we have a rapid distribution to as many as possible," Mr Hunt said.
"By definition, somebody has to be first. And we will celebrate every vaccination, and we want as many people to be vaccinated as possible. So, every vaccination will be a cause for celebration. Let me say this - we know that as you vaccinate a country, it will take time and some people will want to be earlier. We've seen some examples of that. But the medical advisors who have protected us over the course of this last year - exactly this last year, are the ones who are continuing to provide the advice on the vaccine rollout."
The vaccine rollout will start across up to 50 hospital sites across the country.
The vaccine will be rolled out in five stages in coming months and will have 1000 vaccination sites operational.
TGA says job isn't finished
Health Minister Greg Hunt welcomed the news of the TGA's approval.
"Australia's high bar has been met; the vaccine has been approved as effective in stopping severe disease," Mr Hunt said.
"I thank all those involved in the development and assessment of this COVID-19 vaccine, including the researchers, Pfizer, BioNTech and the medical experts at the TGA who have worked around the clock and over Christmas.
"This approval and the upcoming roll out of the vaccine will play an important part in our ability to manage the pandemic in 2021."
The head of the TGA, Adjunct Professor John Skerritt, said work had been non-stop in carrying out tests for the vaccine to meet approval standards.
"We're thrilled to have this product pass the rigorous regulatory process and receive provisional approval," he said.
"Our job is by no means done. In fact the monitoring of vaccine safety post-approval is an important part of the regulatory review of vaccines.
"We now check the individual batches of vaccines that are destined for Australians while closely monitoring the safety and efficacy of the vaccine as it is rolled out."
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