The federal government has signed a deal with AstraZeneca for nearly 54 million doses of the vaccine in 2021, with 20 million to be produced in Australia by CSL.
It comes after Britain became the first country to approve a coronavirus vaccine developed by Oxford University and AstraZeneca, hoping rapid action will help it stem a surge of infections driven by a highly contagious variant of the virus.
It was the first to approve a shot developed by Pfizer of the United States and Germany's BioNTech, with the result that hundreds of thousands of people were vaccinated in Britain before EU countries and the US even began administering it this month.
While the approval by the UK Medicines and Healthcare products Regulatory Agency (MHRA) is a vindication for a shot seen as essential for mass immunisations in the developing world as well as in Britain, it does not eliminate questions about trial data that make it unlikely to be approved so rapidly in the EU or the US.
Uncertainty has swirled over the most effective dosing pattern for the AstraZeneca/Oxford vaccine since it released data last month showing a 90 per cent success rate for a half-dose followed by a full dose, but only 62 per cent - still usually more than enough for regulators - for two full doses.
The MHRA said that the results for the half-dose regimen had not been borne out by analysis. Instead, it approved the regimen of two full doses.
An official involved in the MHRA decision, said that the vaccine's effectiveness had risen when the doses were given three months apart.
"Effectiveness was high, up to 80 per cent, when there was a three-month interval between first and second doses, which is the reason for our recommendation," Munir Pirmohamed, Chair of the Commission on Human medicines expert Working Group on COVID-19 vaccines, told reporters.
Storage and delivery advantages
Molecular virologist Dr Keith Chappell at the University of Queensland said Astrazeneca's lower success rate compared to the Pfizer vaccine, which recorded a 95 percent in its trials, is not an issue.
"Sixty percent efficacy is still a fantastic number. It is much better than a lot of the flu vaccines," he told SBS World News.
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Astrazeneca's vaccine can also be stored at lower temperatures compared to the Pfizer doses, which need to be stored at the ultra-cold temperature of -70 degrees Celsius at all times.
"It could be such a logistical nightmare [to transport the Pfizer vaccine]. Astrazenca's vaccine is refrigerated and has that huge advantage that it can be transported to reach multiple areas ... out to regional communities."
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Additional reporting: Reuters