Federal Health Minister Greg Hunt confirmed the Australian Technical Advisory Group on Immunisation (ATAGI) has recommended a change in advice after a second Australian, a 52-year-old woman, died after developing a rare case of blood clots associated with the vaccine.
"They have recommended an increase in the age range for those who should be using AstraZeneca from 50 to 60 and above," Mr Hunt said.
"And they have therefore recommended that Pfizer is the preferred vaccine for under 60s."
Mr Hunt said the roll-out was still "on track", but he conceded it was a "challenge".
"It's a challenge, every day, every day during COVID," he said.
"The world has challenges. Australia's challenges, thankfully, mercifully have been different to the rest of the world."
Until now, the AstraZeneca shot was only to be given to people aged 50 and above.
The Health Minister has spoken to the Australian head of Pfizer on Thursday about the issue of supply.
The military-led rollout has now been given the name, "Operation Covid Shield" and 2.8 million doses of the alternative COVID-19 vaccine from Pfizer are now due next month.
"We will have access to 2.8 million doses during the course of July, which is in excess of what we had previously indicated. So that is positive," Mr Hunt said.
"We were previously expecting 600,000, it has been increased to 2.8 million. We have also requested that anything which can be brought forward, should be brought forward. It is a difficult, challenging global situation."
ATAGI has also recommended that second doses be completed for all those who have had AstraZeneca who are under 60 years of age.
Australia's COVID-19 vaccine rollout is set to be thrown into further chaos, with the government's vaccine advisory body to recommend the AstraZeneca vaccine should only be given to those aged 60 and older.
State and territory health ministers will hold an urgent meeting on Thursday to consider the next steps in the COVID-19 vaccine rollout based on the advice from the Australian Technical Advisory Group on Immunisation.
Until now, the AstraZeneca shot was only to be given to people aged 50 and above, but last week a 52-year-old woman died after developing blood clots associated with the vaccine.
The AstraZeneca vaccine, developed by Oxford University, was set to be the major pillar of Australia's vaccine rollout, with Melbourne-based CSL signing a deal to produce the vaccines onshore.
But when concerns were raised in European countries over rare but serious blood clotting conditions developing in the weeks after receiving the first jab, in April the Australian government was forced to recommend only people aged over 50 get the vaccine.
That decision was based on the higher risk to people aged over 50 if they get COVID-19, and the higher risk of blood clots in younger people after receiving the vaccine.
According to the Health Department, the risk of developing the side effect is low and "may occur in around 4-6 people in every million after being vaccinated with AstraZeneca".
Speaking at a press conference on a new outbreak of COVID-19 in Sydney, NSW Chief Health Officer Kerry Chant didn't confirm the advice had been changed.
"I have not been briefed on the specifics of that advice but generally, we follow the ATAGI advice," she said.
"Those experts have the best information and we appreciate the work we have done in reviewing all the international evidence in providing that expert advice."
The likely change in advice will put further pressure on Australia's supply of Pfizer vaccines, the only other vaccine against COVID-19 currently approved and available in Australia. That vaccine must be imported from overseas, and while supply is expected to increase starting next month, large amounts of the vaccine aren't expected until at least September.
More to come
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