Australia is now seeing the start of a new wave of COVID-19 infections, driven in part by new sub-variants of Omicron.
On Friday health authorities said that over the last week, 54,661 cases of COVID-19 have been reported across Australia.
That's an increase of 47.3 per cent on the previous week.
This week, case numbers in Queensland almost doubled, prompting the state government to recommend masks again be worn again in some settings.
And in New South Wales, numbers have also spiked, with 19,800 cases detected in the seven days to 4 pm Thursday.
That's up by 7,350 compared to the week before.
But given we've moved on from mandatory reporting and PCR testing, how much our reported caseload can really tell us about the spread of the virus is limited.
Experts believe the reported case numbers are substantially lower than the actual level of infections.
But they say we can still glean valuable information from the data if we change the way we interpret it.
Can we rely on the numbers we're hearing?
It's complicated.
It's no longer mandatory to register a positive COVID test in many states.
It also isn't mandatory in all states and territories to test if you have symptoms, so we can't be sure how many people are testing when they get ill.
However, Professor Ian Marschner — a biostatistician at the University of Sydney — said what the figures do provide is an overview of what's happening in the community.
"They're definitely less reliable than back when everything was reported by PCR," he said.
"So, while it's probably true that the numbers of case diagnoses, numerically, are less reliable than they have been in the past, I think we can rely on the directional trends.
"That should then, I guess, be used to refocus our efforts on some of the sensible control measures that we can use."
Why else aren't the numbers as reliable anymore?
A few reasons.
There are people who know they had COVID but didn't report it; people who had symptoms but didn't test; and people who had the virus but didn't have symptoms.
Even during previous waves, the reported case numbers likely didn't match the actual infections.
According to a recent blood study looking at how many people had developed antibodies to the SARS-CoV-2 virus, about two thirds of the population are like to have already been infected.
That's a far higher infection rate than what was reported to authorities.
So, how much higher could it be now?
"It could be 50 per cent more, 100 per cent more, even 200 per cent more," said Professor Adrian Esterman, chair of biostatistics and epidemiology at the University of South Australia.
"We simply don't know."
Where are things headed?
The data available from the states and territories point to infections heading in one direction: up.
But working out how bad it could get is harder than before.
Professor Esterman said the available data showed a huge increase in cases over the last week, but many factors make predicting how bad it will get tricky.
He said a number of Omicron sub-variants were in circulation and it wasn't yet clear how much more transmissible they were, or how easily they could evade the immune system.
Added to that is the difficulty in working out how much protection was being provided community wide by vaccines and prior infection.
Professor Esterman said some people were unvaccinated, while others have had anywhere between one and five doses, each offering their own level of protection.
"We've got a very mixed population," he said.
Professor Marschner agreed, and thought Australia's high vaccination rates could make this wave shorter than those of the past.
"After an initial peak, it will subside. It's very difficult to predict exactly how quickly that will happen.
"But if we compare it to earlier on in the pandemic, obviously there is much better vaccination coverage and focus on the various control measures."
Is there anything we can do to stem the spread?
Yes.
State and territory governments have removed most of the restrictions in place to limit the spread of the virus, but some experts would like to see a few of them come back.
"Isolating when you're infected will certainly help control the spread of the virus," Professor Marschner said.
"So, from an epidemiological perspective, I think that is clear. Now, from an economic and political perspective, I guess there are many other dimensions to the problem.
"But [isolation] could be looked at as a potential way to turn the curve over."
Sanjaya Senanayake, an infectious disease physician at the Australian National University, is also optimistic.
"We've got the experience of Singapore, who recently had a new sub-variant dominating their landscape," he said.
"They did have a rise in cases, they did have a rise in hospitalisations, but it was a fairly short peak and they are starting to see numbers dwindle.
"So, I am hopeful that with our good immunity due to a combination of having had COVID and having high rates of vaccination, at least with two doses, we should have a similar pathway to Singapore."
