Australians under the age of 50 will be recommended against receiving the AstraZeneca vaccine, after a link was confirmed between the jab and rare blood clots.
European authorities have identified the link, prompting the United Kingdom to offer people aged under 30 an alternative vaccine due to the risk.
The Australian Prime Minister received a series of recommendations from the Australian Technical Advisory Group on Immunisation on tonight, after the country's drug regulators held urgent meetings to consider the findings.
Chief among them is that the Pfizer vaccine should now be adopted as the preferred vaccine for people aged under 50.
The recommendations are made under an "abundance of caution" of the rare but serious side effects mostly associated with younger people, Prime Minister Scott Morrison said.
"We've been taking the necessary precautions based on the best possible medical advice," he said.
"It has not been our practice to jump at shadows."
ATAGI also recommended those under the age of 50 who have received their first AstraZeneca jab will proceed with their second, as the medical advice indicates the rare blood clots only develop after the first dose.
Only where the benefit clearly outweighs the risk should an initial AstraZeneca dose be administered to someone under the age of 50.
Health care workers aged under 50 who were due to receive the AstraZeneca vaccine will now be prioritised for the Pfizer vaccine, which will likely delay phase 1b of the rollout.
The findings will also be discussed among state and federal health ministers and at the next meeting of national cabinet tomorrow.
More than 996,000 coronavirus vaccine doses have now been administered.