Ms McArthur raised the issue, uncovered by The Standard, that the Burnet Institute modelling underpinning the roadmap only models metropolitan Melbourne.

"When Daniel Andrews claimed that the roadmap was based on the Burnet Institute's modelling, did he forget that Victoria's borders do not end at the Ring Road or did he just mislead the public?" she said.

The issue was also put to Minister for Education James Merlino when he announced details of regional Victoria's back to school plan.

Mr Merlino disputed the fact the Burnet modelling only looks at Melbourne, seemingly contradicting Burnet Institute head modeller Dr Nick Scott as well as the Department of Health, which had previously confirmed the modelling was confined to metro Melbourne.

"I don't think that's right... the Burnet modelling, and the broader public health advice looks at the epidemiology of the situation across the whole of Victoria," said Mr Merlino.

The minister was asked to revise or clarify his comments in light of the contrasting evidence, but he declined to respond.

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In response to follow up questions from The Standard, the Department of Health said it "draws on large amounts of data, including modelling, to determine the public health measures".

The department said it was difficult to model regional Victoria, which had few cases over a large geographical area.

Public health officers remain fearful of a regional outbreak that could paralyse the local health system, such as occurred in Mildura, or plunge much of the community into isolation, as occurred in Shepparton.

Those concerns, combined with a lack of scientific data, are the reason many regions are having to cope with apparently harsh restrictions.

The department declined to share any specifics about the additional data or modelling it said was being used to develop regional public health measures. It is unclear why the Burnet modelling has been shared with the public while the regional data and analysis has been suppressed.

The Minister for Health has 30 days to respond to Ms McArthur's request for more information.

Melbourne University epidemiologist Professor Tony Blakely said it was possible to model regional areas accurately, but it was very difficult.

"You could do it, you could build a really flash model for it, but it would take too long," he said.

Professor Blakely, who has worked on COVID-19 modelling for the state government, said it was important to remember modelling didn't provide black and white answers.

"The way to think about modelling is that it creates a structured way of thinking, getting a feel for what you should do," he said.

He said the infectiousness of the COVID-19 Delta variant made it even more difficult to model.

"What we've seen recently is the spread has been in specific populations and specific areas, rather than others," Professor Blakely said.

This phenomenon, where particular groups have different levels of risk, is called heterogeneity. "Trying to anticipate it is hell," he said.

"Modelling only goes so far, there's only so much you can do."

But he said modelling still provided valuable guidance, meaning the lack of modelling in regional areas created an extra layer of guesswork when developing the roadmap.

Professor Blakely said it was possible areas like Warrnambool were more restricted than necessary, but he warned against throwing off the shackles.

"We find if you don't keep up a minimum level of restrictions then it's not pretty.

"Once we get to 80 per cent fully vaccinated we can chill out a bit," he said.

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