Another 7.5 million Australians are becoming eligible for a fourth COVID-19 vaccine as new Omicron sub-variants drive higher case numbers and hospitalisations around the country.
The Australian Technical Advisory Group on Immunisation (ATAGI) has recommended the shot for people over 50, while those aged 30 to 49 may choose to have a fourth dose.
In announcing the expansion of the COVID vaccination program, Health Minister Mark Butler said there was "a strong case" for older Australians to receive the additional booster shot but an "open question" about whether younger, healthy people needed it.
With that in mind, you might be asking whether or not you should be rushing to book an appointment at your GP or local pharmacy for your fourth dose.
Is it worth getting a fourth vaccine dose?
The ATAGI advice is that those already eligible, including people aged over 65, remain at high risk of severe disease and death from COVID-19.
The position of the Royal Australian College of General Practitioners (RACGP) is that the expanded eligibility for a fourth dose will help reduce the risk of severe illness, ICU admissions and deaths, and relieve some of the pressure on hospitals.
James Trauer is the head of epidemiological modelling at the School of Public Health and Preventative Medicine at Monash University.
He says while there isn't an Omicron-specific vaccine available yet, the existing vaccines still offer a good level of protection.
"There's going to be a lot of transmission over winter and there's going to be a lot of hospitalisation, so I would say, on balance, get vaccinated now if you're concerned," Dr Trauer said.
"As we head towards an endemic state, we need to protect people from infection rather than trying to control transmission."
But he said it was an individual decision for younger, healthier Australians.
"These vaccines don't control transmission the way they used to so it's more about your own assessment of risk and protecting yourself against the worst outcomes of the virus," he said.
"I think a lot of people in the 30- to 59-year age group will benefit, particularly people towards the 59-end of the spectrum.
"Also, people who are longer from their last vaccine, if they've had the third dose many months ago."
But Australian National University public health and infectious disease expert Katrina Roper said there was not enough evidence at the moment to definitively say whether the fourth shot provided any additional protection for the under 65s.
"There isn't an enormous amount of data to indicate it could be useful but at the same time this is an evolving situation and someone has to be putting this into effect to see if it will be effective," Dr Roper said.
However, she welcomed the announcement of the expanded eligibility.
"Five million people have only had two doses and they should have had a third," she said.
"By saying that you're now eligible for a fourth, that might actually make them get a wriggle on and say 'well, before I was only one dose low, now I'm two doses'.
"That would be really helpful."
Will the fourth dose provide protection against BA.4 and BA.5?
Pfizer and Moderna's mRNA vaccines are ATAGI's preferred vaccines.
The AstraZeneca vaccine can be used when someone cannot have an mRNA vaccine for medical reasons or if they decline one, while Novavax is also approved for a fourth dose, but only if no other vaccine is considered suitable for the patient.
Nathan Grills from the Nossal Institute of Global Health said the vaccines provided the same level of protection against BA.4 and BA.5 as the earlier Omicron sub-variants, with good evidence a fourth dose gave two to four times more protection from severe disease in older age groups.
"ATAGI's suggestions I think are in line with the evidence and also wise given we're seeing a rise in cases and a risk in hospitalisations and stress on our health system in Australia," Professor Grills said.
Dr Trauer said Moderna would have a vaccine available in coming months that will target the Omicron variant.
"But it really targets the earlier versions of Omicron and we're already looking at BA.4 and BA.5," he said.
"The vaccines we have do offer protection now and we have to work with what we have, otherwise we're just going to be chasing our tail forever and always waiting for the vaccines to keep up with the viruses."
He said people concerned about their risk with the high transmission should act now.
But Professor Grills said there was a case for those over 30 who are healthy to delay their fourth dose in the hope of the Omicron-specific vaccines could be more effective.
"Many of us have had an infection of COVID recently," he said.
"If you've had three doses and you're thinking about a winter booster dose and you've also had COVID a month ago, then waiting might be a wiser idea given there might be more Omicron-specific vaccines coming out that might be even more effective against the current strains that we're seeing."
"It's a person-by-person situation.
"I'm 40-something and I've booked my vaccination in the near future."
What can we learn from overseas?
Israel began offering a fourth dose in early 2022.
Dr Trauer said it had demonstrated good protection against severe illness.
"They were dealing with probably different variants than what we're dealing with now but generally, on the whole, vaccines have held up to the virus mutating," he said.
Professor Grills said the data showed a fourth dose increased protection from catching the virus at first, but it waned after a month.
But he said it clearly was shown to provide three-to-four times higher protection from severe disease, compared to having three doses.
"The significant protection against severe disease, and probably against long COVID, in the over 60s that we've seen in the US, Israel, UK, Canada in the data and studies there will probably be also experienced in the younger age group of 30 to 50, that similar level of protection," Professor Grills said.
Can you have too much vaccine?
Dr Trauer said all vaccines and medications can cause side effects.
But he said the COVID vaccines were "generally safe and generally have retained their effectiveness".
He said he believed that over the next year or two, we would no longer talk in dose numbers.
"The question is going to become 'how long is it since your last dose?'"
"When we head into these substantial waves, if we get new variants, if we're heading into winter and risky months, it's the people that haven't been vaccinated for a couple of years and are at high risk that we should be targeting."
What about kids who can't get a first or third dose?
Children and teenagers under the age of 16 are still not eligible for a booster shot and those under five haven't received any vaccinations at all, so should we be talking about giving fourth doses to adults?
Dr Trauer said parents and carers have no need to worry.
"Their risk is so low. It's not a consideration from a public health standpoint, it's not really a consideration from a hospitalisation standpoint except in particular vulnerable groups.
"If you're a healthy three- or four-year-old, your risk of a severe outcome is really, really tiny."
Likewise, Dr Roper said she did not think eligibility for a fourth dose would be expanded to the under 30s any time soon.
"If it's not going to be recommended it's because it's not shown a demonstrable benefit and therefore would rather people take other actions which is be safe, think about your behaviours and encourage those who would benefit to get their vaccinations," she said.
What if I've recently had COVID?
The Department of Health has recommended Australians wait three months after a COVID-19 infection before getting a vaccination shot.
The government states while there are no safety concerns about having a vaccine dose within three months of an infection, an appropriate gap will lead to a better immune response and longer protection.
Immunocompromised individuals or those travelling overseas who will not have access to the vaccine may be vaccinated earlier than the recommended interval.
