Australia is expecting a short-term slowdown in its already sluggish coronavirus vaccine rollout after new advice on the AstraZeneca jab.
Medical experts are now recommending people under 60 receive the Pfizer jab.
The Australian Technical Advisory Group on Immunisation determined the risk of extremely rare but serious blood clots outweighed AstraZeneca's benefits among that cohort.
Health experts are urging the 840,000 people aged 50 to 59 who have had a single AstraZeneca dose to have their second jab.
The extremely rare blood clotting condition, which has led to two deaths from 3.8 million doses in Australia, almost always only occurs after the first injection.
People in the 50-59 age bracket will be able to claim a bulk-billed GP consultation about the jab through a newly listed Medicare item.
Health Minister Greg Hunt remains confident about Pfizer supplies even with the increased reliance on the imported vaccine.
Mr Hunt said re-booking people in their 50s who were down to get a first AstraZeneca jab would likely lead to a fall in vaccination rates.
"The interesting point here was that some in that group, who were not intending to be vaccinated in the near term, may well choose to be vaccinated," he said.
Australia continues to lag behind much of the world in vaccination rates with around four per cent of adults receiving both doses.
But just one person is in intensive care nationwide with the international border closures and other health measures keeping the virus at bay.
Lieutenant General John Frewen, who is overseeing rollout logistics, said the slowdown would be short term but refused to say whether that meant weeks or months.
"We will see a likely temporary reduction in daily vaccination rates, as people make informed decisions around what they want to do in light of the ATAGI announcement," he said.
"This potential reduction should be short term and then we would see a return to the more regular daily vaccination rates."
National cabinet will meet on Monday to discuss what the increased reliance on Pfizer imports means for the immunisation program.
Chief Nursing Officer Alison McMillan said there were no plans to switch to a "mix-and-match" approach of recommending individuals receive different vaccines.
"The evidence is very low at this point in time on the efficacy of that," she said.
Labor has seized on the rollout's latest setback to reignite its argument the government relied too heavily on AstraZeneca.
Deputy Opposition Leader Richard Marles said the latest Victorian lockdown and an emerging Sydney outbreak showed the importance of ramping up jab rates.
"We are going to be living in the land of the lockdown until we get vaccinated," he told the Nine Network.
Chief Health Officer Paul Kelly said receiving both doses was important to ensuring people were fully protected against the disease which has killed at least four million people globally.
Australian Medical Association president Omar Khorshid said doctors had developed effective treatments meaning most people who developed the rare clots recovered fully.
Australian Associated Press