More than one third of older Australians most vulnerable to serious COVID-19 infections are yet to get boosted, and nearly half of them have been eligible for their third dose for at least a month.

As ATAGI approves the Pfizer vaccine booster for 16 and 17-year-olds, the federal government released new data this week showing booster coverage in each age group as of Monday. The new data shows a significant number of people across all age groups have been eligible for their booster for weeks, but are yet to get it.

No age group is more than two-thirds boosted, but coverage among people in their 70s and 80s, who have had the longest to get their third shot, has exceeded 60 per cent.

Kirby Institute epidemiologist Greg Dore said he was surprised that more than a third of the 70+ population is unboosted.

"The number one priority, absolutely, has to be to optimise the coverage among older and vulnerable populations, while also encouraging younger people to come forward," Professor Dore said.

"We had this incredible urgency during the Delta wave, we just don’t seem to have that same sense of urgency now, despite there being more deaths than at the peak of the Delta wave."

Coverage in the general population is lower than coverage among the smaller group of aged care residents.

The Prime Minister yesterday said that while 99 per cent of aged care homes had been visited by a booster clinic, only around 70 per cent of residents had actually been boosted.

The Minister for Health and Aged Care Greg Hunt told RN Breakfast that some residents or their families are "making their own choice" not to get boosted.

"My gentle message to families is please, please, please, allow your residents, your families, your loved ones, to have that booster," Mr Hunt said.

He did not put a figure on the number of people who have declined a booster.

These groups have low booster uptake

Booster coverage is much lower among people under 40, where less than 30 per cent of people have had their shot.

Only about 15 per cent of people in their early 20s have received a third dose.

But they have also had less time to get boosted, given younger people had to wait longer to get their first dose.

Many only became eligible this week, when the booster interval was reduced to three months nationally.

One way to control for that difference in access is to consider how many people are unboosted well after they became eligible.

People who got their second dose more than four months ago have been eligible for a booster since at least January 4.

“There is no doubt that waning [immunity] is a real issue … the longer the period from completion of two dose vaccination increases the risk of hospitalisation and mortality clearly, particularly in the older age group,” Dore said.

About 16 per cent of people in their 80s got their second dose more than four months ago, which means they have been eligible for a booster since at least January 4.

That group makes up more than 40 per cent of all unboosted Australians in their 80s.

On that measure, across each age group there is a similar share of people well past eligibility for their third dose.

People in their 40s and 50s appear to be the most likely to be falling behind in getting boosted.

Omicron infections have delayed boosters

The other complication in the booster rollout is that the Omicron wave of infections has delayed third doses for many, as they were becoming eligible.

For example, roughly 10 per cent of the NSW population have tested positive since the start of summer.

That disproportionately affects young people, given that infections in this wave have skewed younger.

People in their 20s and 30s have consistently been most likely to test positive on a PCR.

Authorities say an infected person can get their third dose after they’ve completely recovered, and NSW Health says that is after about four to six weeks for most people. 

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And while the top priority for boosters should be the people most likely to suffer serious consequences of infection, ATAGI advisory committee member Kristine Macartney says moving beyond the acute crisis relies on broad coverage for all.

“In terms of how we leave pandemic conditions, it is about building immunity, turning this into a milder virus for many of us,” Professor Macartney told ABC News.

“It's about where we do have our most vulnerable, who will still be at risk of serious disease, having treatments and managing those patients.

“That's growing all the time, as is immunity through booster vaccinations and that is why boosters are so important.”