A fifth vaccine is available in Australia for people who are severely immunocompromised. 

Winter is coming and the federal government says it's getting prepared to ensure Australia is in the best position when it comes to COVID-19. 

This includes seeking advice from the Technical Advisory Group on Immunisation (ATAGI) on a fifth vaccine dose.

It's currently available in Australia for adults who are severely immunocompromised, but ATAGI is considering whether to approve it for more people. 

But before we get to the fifth dose, let's look at how many Australians have already been boosted and how many doses authorities are recommending.

How many people have had each dose? 

When it comes to the first vaccine, about 20 million people have had it, according to data from the department of health and aged care. 

And about 19.8 million people have gone back for their second dose. 

Of those eligible, 14.3 million people have had their third dose.

And the data shows 5.4 million people have had number four.

Or, as a percentage of eligible Australians, it looks like this:

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So, we know fewer people have had their fourth dose but how important is that number and what does it tell us?

Monash University associate professor James Trauer says it's actually more relevant to look at how long it has been since someone had their last vaccine than how many doses they've had in total.

ATAGI recommends people wait at least three months between boosters, and while there is no upper limit to the time you take between them, it says vaccine effectiveness wanes over time. 

Dr Trauer says the effects start waning after the first month and vaccines have less effect in the following three, six and nine months. 

Because of this, he says it's important Australians are topped up ahead of another wave.

He says this is especially important for the elderly and vulnerable who were among the first to be vaccinated and boosted.

The focus of public health messaging should be on vaccination and early detection for people in vulnerable groups who are eligible for antiviral medications, Dr Trauer says.

You can check out who's eligible for antivirals here.

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So, what changes could be ahead?

Health Minister Mark Butler says the federal government is expecting to get advice from ATAGI about the fifth dose "very early this year".

He says Australia needs to think about an additional booster as we approach April, May and June.

"They [ATAGI] and governments are thinking about the need to be prepared for the next winter," he told 7.30.

Paul Griffin, who is the director of infectious diseases at Brisbane's Mater Hospital, says considering a fifth dose is the right move.

"I think there's lots of people that want to get another dose, those people that had their last dose some time ago and people who might have a perceived increased risk, whether they're travelling, or working in a high-risk role, for example.

"So, we don't want to boost people again too early, but I think they're all the things ATAGI are considering and that should lead to another dose fairly soon."

Dr Trauer says while it is likely a pattern for winter COVID-19 epidemics will form in the future, he doesn't believe we have reached that stage. 

He says the recent waves have been driven by new variants rather than the seasons. And that's likely to continue.

Rather than watching the weather radar, Dr Trauer is keeping an eye on the Omicron subvariant XBB.1.5, which is spreading across the United States.

It "looks concerning" and "could cause an epidemic" in Australia, he says.

How many doses should I have?

One booster — a third dose — is recommended for all people 16 and over, three or more months after the first two vaccines. 

For kids between five and 15, a third dose is only recommended for those who are severely immunocompromised, have a disability or complex health needs, or if they have a condition that increases their risk of severe COVID. 

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A second booster — dose number four — it is recommended for people over 50 and those over 16 who live in an aged or disability care facility, as well as people over 16 who have a health condition or a disability that increases their risk and the impact of COVID.

Those between 30 and 49 can also have a second booster, but the benefits are less certain and a chat with a health professional is recommended. 

A booster is not recommend for children under five or for those who are between five and 15 who don't have an increased risk. 

What vaccine am I eligible for?

For adults under 60, Pfizer, Moderna, or Novavax are preferred by ATAGI over AstraZeneca for the first two doses, while there is no preferred brand for people over 60. 

For pregnant women, Pfizer and Moderna are recommended and Novavax is also an option, but AstraZeneca is not preferred.

When it comes to kids between six months and five years old, COVID vaccines are only recommended for those who are severely immunocompromised, who have a disability or those who have a severe risk of severe COVID-19.

When it comes to what kind of booster you get, the Pfizer vaccine is the only one that is approved for kids from five to 17.

There are more options for adults: Pfizer original, Pfizer bivalent, Moderna original and Moderna bivalent are all available. 

And although it is not the preferred option, AstraZeneca and Novavax can be used as boosters for adults in certain circumstances. 

While it not TGA-registered, Novavax can be used as a booster for a person who is at least 12 years old when no other brand s suitable for them.