On the face of it, it seems confusing: data shows there are more vaccinated people than unvaccinated people in ICU in Victoria and New South Wales.
Taken out of context, it can contribute to misinformation or even give an incorrect picture of how effective vaccines are.
But experts say that given the vast majority of Australians are fully vaccinated, the data is not surprising.
We take a look at the figures, and why some people are still suffering adverse outcomes despite being fully vaccinated.
Unvaccinated people are still over-represented in hospitals, death figures
If you look at raw NSW intensive care numbers in isolation with no other context, it can seem counterintuitive.
Between November 26 and January 8, 215 double-vaccinated people were admitted to intensive care, compared with 55 unvaccinated people, according to a recent COVID-19 surveillance report.
But those 215 people make up less than 0.1 per cent of fully vaccinated COVID-19 cases recorded in that period, while the 55 make up about 1.5 per cent of unvaccinated cases.
That might not sound like a big difference, but it's like a 1 in 1,000 chance of being admitted to intensive care if you're double vaccinated, versus a 15 in 1,000 chance if you're unvaccinated.
In other words, if you contract COVID-19, you're 15 times more likely to end up in ICU if you aren't vaccinated.
"The key issue really is not so much the percentage of people in ICU that have a given vaccination status," said Ian Marschner, a professor of biostatistics at the University of Sydney.
"The key issue is really to what extent are unvaccinated people over-represented in ICU? And to what extent are vaccinated people under-represented?
"And it's the relativity of those two things that really gives you information about whether vaccination is protecting against going into ICU."
A similar story is playing out in other parts of Australia.
The NT government recently said unvaccinated people made up about half of people in intensive care, despite making up a much smaller part of the population.
Queensland's health minister also recently reported that unvaccinated people made up between 20 and 30 per cent of COVID-19 deaths, despite making up just 8 per cent of the population.
According to a recent Victorian Chief Health Officer update, unvaccinated people accounted for 22.8 per cent of people in hospital and 35.8 per cent of people in ICU, despite making up less than 6 per cent of the population.
"This data clearly shows that a COVID-19 case is far more likely to be admitted to hospital or ICU if they are unvaccinated, and far less likely to be admitted if they have received three doses of the vaccine," the update said.
Anthony Holley, from the Australia New Zealand Intensive Care Society, said it was important not to let an out-of-context read of COVID-19 data convince anyone that vaccines were not effective.
"There is a relatively small group of the vaccinated patients that are indeed ending up in ICU. And this speaks to the efficacy of the vaccine," he said.
Why are some fully vaccinated people still going to ICU?
The vast majority of Australians are now double vaccinated. But even though vaccines reduce the risk of becoming seriously ill if you get COVID-19, no vaccine is 100 per cent effective.
"Very rare events, such as getting critically ill when you're double-vaxxed, still will occur when you've got millions of people [who are vaccinated]," said Stephen Warrilow, the director of intensive care at the Austin Hospital in Melbourne.
There are also some medical conditions that mean people are unfortunately more at risk of adverse outcomes from COVID-19, even when they are vaccinated.
That includes transplant recipients, whose immune systems are suppressed because of medication to stop their body rejecting the organ, as well as people with certain types of cancers.
"It's a tough time for people who are immunosuppressed at the moment because they can sort of do everything right, and they can follow all of the health advice and be doing quite well ... and they can still sometimes get quite sick," Dr Warrilow said.
Other risk factors for COVID-19 include obesity, older age, heart disease, and conditions like chronic obstructive pulmonary disorder (COPD), according to Jaya Dantas, a professor of international health at the School of Population Health at Curtin University in Western Australia.
During the Delta outbreak, most people in ICU were unvaccinated. Why the change?
Professor Marschner said there was one "key difference" between the Delta and Omicron outbreaks: the percentage of unvaccinated people in the community.
Back in early September, when NSW's Delta outbreak was at its peak, less than 50 per cent of the eligible population in the state were double dosed.
When the Delta outbreak peaked in Victoria around mid-October, less than 70 per cent of people over 16 had received their second dose of the vaccine.
By the time Omicron arrived in Australia in late November, more than 85 per cent of eligible Australians were fully vaccinated — and that number has continued to grow.
"During the Delta outbreak, we were really ramping up our vaccination coverage. Whereas with the Omicron outbreak, we're coming from a high base of vaccination coverage," Professor Marschner said.
"As we were ramping up our vaccination levels from very low levels to higher levels, we did expect a greater percentage of ICU patients to be unvaccinated."
At the time of writing, more than 93 per cent of Australians over 16 have had at least two doses of a COVID vaccine.
Professor Dantas said when looking at COVID-19 data, it was important to look at the "bigger picture" — which was that the vast majority of fully vaccinated people were not getting seriously ill with COVID-19.
What does this mean for vaccines?
Another factor that could contribute to how COVID-19 affects vaccinated people, is how much time has passed since getting a second dose.
"The further you get from that second dose, the less likely you are to have a level of protection either against infection or severe disease, or symptomatic disease with Omicron," said Kylie Quinn, an immunologist and Vice Chancellors Research Fellow at RMIT University.
"From about five months after that second dose, then you start to see really significant waning."
People who were vaccinated early on in Australia's vaccine rollout, also tended to be people who were at higher risk from COVID-19, such as older people or those with underlying conditions, Dr Quinn said.
"They will have experienced more waning than people who got their second dose a little bit later in the rollout," she said.
Evidence also shows that Omicron is more likely to evade vaccines than previous variants of COVID-19.
This is why many experts, including state chief health officers, say it's important for people to get booster shots as soon as they can.
"I can't be clearer that a booster is essential in providing and maximising your protection against the Omicron variant," NSW Chief Health Officer Kerry Chant said.
"Two doses against the Omicron variant are not sufficient — you need the third dose. So anyone thinking that two doses is enough, I can't be clearer — please get that booster dose, and get it as soon as possible."
