Our winter surge was 'deep-water wave', expert says.

Multiple COVID-19 variants are circulating in Australia and could be adding to the risk of re-infection.

Deakin University chair of epidemiology Professor Catherine Bennett said a mix of variants could be "cycling" illness in the population.

And immune systems were struggling to build the antibodies to keep up, she said.

Wastewater and PCR test results in Victoria from July 14 show 83 per cent of infections were from COVID-19 XBB lineages.

This included XBB.1.16, responsible for 30 per cent of infections and XBB.1.5, which caused 12 per cent of cases.

CH.1.1 or "Orthrus" accounted for five per cent of Victorian infections.

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More people died in winter generally and a range of COVID-19 variants added "more pathogens in the mix," Professor Bennett said.

"The most recent surge hasn't reached the previously high daily report numbers but it's what I call a 'deep-water wave'," she said.

"It doesn't go as high but it surges," Professor Bennett said.

"And you end up with a lot of people under the curve but infected over winter," she said.

Between July 10 and July 17, 8,047 cases of COVID-19 were reported across Australia with an average of 1,150 cases per day.

Professor Bennett said Australia would likely have a number of infections in the community that were flying under the radar because they weren't severe.

Almost all COVID-19 cases in Australia stemmed from the highly infectious Omicron variant including XBB, XBC and CH.1.1.

XBB.1.16, or Arcturus, has "levelled out over the past couple of months," Professor Bennett said.

"It's still the most dominant because it's the newest XBB variant," she said.

New variants tended to be responsible for more infections and XBB.1.5, which surged in March and April, had declined, she said.

A non-XBB variant, CH.1.1 or "Orthrus," had been responsible for 5 to 10 per cent of infections nationally since the start of the year, Professor Bennett said.

And the XBC strain had been "growing in the background" since the beginning of 2023 but had accelerated this winter, she said.

All strains were "about the same" in terms of severity, she said.