Up until now, we've often thought being fully vaccinated meant having two jabs.
Then, we've all been encouraged to have a "booster", or an extra shot of vaccine.
Now the group of experts that advise the federal government on vaccines has signalled two shots alone won't cut it.
ATAGI is getting rid of the concept of being "fully vaccinated" altogether and says a third dose is necessary to be considered "up to date" with vaccinations.
But what does that actually mean — and what will happen next?
We take a look.
What is the advice from ATAGI?
Everyone 16 and over is now recommended to get a COVID-19 vaccine booster dose to maintain an "up-to-date" vaccination status.
The booster dose is recommended from three months after the last primary dose. But if someone doesn't get a booster shot within six months, their status will change to "overdue".
The advice differs slightly for different groups:
- Boosters are not yet recommended for children and adolescents aged 5-15 years. They will be considered "up-to-date" after their primary course of vaccination
- It's recommended that severely immunocompromised individuals aged 5 and over get a third dose of a vaccine in their primary course of vaccination. A fourth dose booster is recommended for those aged 16 and above, but is not required to stay "up to date"
- People who have had a COVID-19 infection should still follow the advice but can defer their next shot for up to four months after their infection
You can mix and match vaccine brands for your booster shots, as long as it's been approved by the TGA for use as a booster.
Will three doses become mandated?
Now that ATAGI has given this advice, it's up to state and territory governments to decide what to do with it.
Businesses could also make their own decisions on whether an "up to date" vaccination status will be needed for their workers and clients.
National cabinet has already agreed it would not mandate booster shots nationally, except for aged care workers.
Some states like South Australia and Victoria have already made three jabs mandatory for workers in certain sectors, such as health care.
Victoria's Premier has flagged that the state could expand its vaccine mandate to require three doses to visit some public venues, like restaurants.
But when asked on Friday, Victoria's Health Minister would not say whether changes were coming.
South Australia's Premier also said the government "would take all of that [ATAGI's advice] into account" before making any decisions.
As of Friday afternoon, other states and territories were also yet to announce any firm plans or changes to their mandate rules.
ATAGI recommended making the new "up to date" advice take effect by the end of March, to give people enough time to adapt to any changes.
Why is a booster dose recommended?
Experts and governments have been strongly recommending booster doses, especially for people over 60 or with conditions that could put them at risk from a COVID-19 infection.
But still — less than half of the eligible population is covered.
And that has health authorities worried that we're not ready for a potential spike in COVID-19 cases in winter.
Vaccines help reduce the risk of getting infected, but the efficacy wanes over time — especially after the five or six-month mark. Many Australians who are most vulnerable to COVID-19 were also among the first to become eligible for vaccination, so more time would have passed since their second dose.
The Omicron variant has also "changed the landscape" when it comes to vaccinations, according to Sanjaya Senanayake, an infectious diseases physician and associate professor at the Australian National University.
The variant is both more transmissible and more likely to evade vaccines.
"We've found that with Omicron, if you've had two doses of a vaccine, your ability to stave off symptomatic infection is pretty low, 20 weeks or so after getting a second dose of vaccine," he said.
"You've still got about 44 per cent protection against being hospitalised, which is pretty good, but a booster helps both with protection against hospitalisation and against getting symptomatic infection."
Nancy Baxter, the head of Melbourne University's School of Population and Global Health, believes ATAGI's new advice is the right call.
"[Three doses] is really what we need to make sure our immunity is as strong as possible against COVID," she said.
What vaccine rules will apply to overseas arrivals?
Australia will be opening its borders to all international arrivals from February 21, as long as they are double vaccinated.
And while ATAGI's new advice was endorsed by national cabinet at a meeting on Thursday afternoon, it will not apply to international travellers arriving in Australia.
But again, how this works in practice will probably come down to each state and territory.
For example, if a state makes a third shot mandatory to access hospitality venues, international and interstate travellers might need to comply if they want to access those venues as well.
Dr Senanayake said it would be "less confusing" if the same advice applied to everyone.
What does this mean for businesses?
Industry groups are largely waiting for advice from the states and territories.
The Australian Retailers Association, an industry body representing more than 100,000 shops, said it had "regular discussions with state and territory governments who will ultimately decide on any changes to their vaccine mandate requirements".
"It's important we have clarity and national consistency and that we continue to see community restrictions unwind as we achieve higher vaccination rates and live with COVID," its chief executive Paul Zahra said.
"This means an eventual, consistent removal of QR code checks, reduction in isolation periods and no return to vaccination checking in stores which has been a highly stressful requirement for retail teams and customers and resulted in an enormous elevation of customer abuse."
The Business Council of Australia, an association that includes chief executives from a range of industries, has also been contacted for comment.
