Half a million Australians will soon roll up their sleeves again, this time for a third dose of the Covid-19 vaccine.
Australia's peak advisory group on vaccines has now officially given the green light for booster shots for those whose immune systems "did not produce the optimal response to the first two doses."
In a statement this morning, ATAGI said the recommendation of a third dose was to address the risk of "suboptimal or non-response" to the standard two-dose schedule for some people.
Authorities say the third dose would maximise the level of immune response to "as close as possible to the general population".
Health Minister Greg Hunt said the group of 500,000 Australians will be able to get their third dose from Monday.
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Those people will need to wait two to six months between the second and third doses, with mRNA vaccines (Pfizer and Moderna) preferred over AstraZeneca.
ATAGI and Hunt said at this stage, there is no recommendation for non-immunocompromised Australians to get a third dose.
"The next stage, the general population stage of the booster programme, we are expecting advice from ATAGI before the end of October," he said.
"But we have over 150 million vaccines secured for the future, and so we are able to implement that on the time frame and the urgency and immediacy that is suggested by ATAGI if and when they provide that.
"I'm not putting a time frame on the booster programme; it's a medical decision. We will follow medical guidance."
Questioned whether booster shots could become a yearly task, like a flu shot, chief medical officer Paul Kelly said at this stage a third dose "would be enough".
"But we are only a year into this [global vaccination effort]," he said.
"A third dose is likely to be the last dose we have to do."
Professor Kelly said people considered immunocompromised included people "with active blood malignancy, blood cancer, people who have had organ transplants and stem cell transplants, people on immunosuppressive therapy".
"There are people who have had transplants who have medications to dampen their immune system, others on certain types of arthritis medication and steroids, those born with immunodeficiency, and a group of people living with HIV who are not controlled under therapy," Professor Kelly said.
"For people in those settings I encourage them to have a discussions with their medical practitioner as soon as possible and book a third dose."
Hunt said the news came as Australia passed the 30 million vaccination mark, with 81.5 per cent of eligible adults having received their first dose and 60.2 per cent are fully vaccinated.
"That means … we've not only passed the USA, but we've also passed Israel and the EU," Hunt said.
"But there is more work to be done, and I continue to urge people to come forward.