Two new Omicron variants are set to become the most dominant in New South Wales as a result of their "growth advantage" over previous strains, according to a new report.
The new COVID-19 Omicron variants— BA.4 and BA.5 — are set to overtake the previously prevalent BA.2 variant in coming weeks, the NSW Health respiratory surveillance report said.
"It is anticipated that in coming weeks the BA.4 and BA.5 sub-lineages, first identified in early April, will become the dominant strains," a NSW Health spokesperson said.
"And will likely be associated with an increase in infections."
Virologist Stuart Turville from the University of NSW's Kirby Institute said BA. 5 was "stickier" than its predecessors because of differences in its spike glycoprotein, which influences how the virus engages with cells.
"BA.5 doesn't look to be a big seismic shift like we saw with BA.1 and BA.2 in comparison to Delta," Professor Turville said.
"[But] the thing we're keeping an eye on with BA.5 is that it's starting to like tissue that pre-Omicron variants like ... it likes proteins on the lung.
"What we want to know now is does it like it as much as Delta and pre-Omicron variants or is it just a bit of a shift from BA.2?"
Infectious disease experts say there is evidence the Omicron sub-variants are effective at reinfecting people with previous infections from BA.1 or other lineages.
There is also concern these sub-variants may infect people who have been vaccinated.
However, there hasn't been a link to an increase in disease severity just yet, although this is being closely monitored, according to the NSW Health report.
Hospital and lab surveillance noted an early start to influenza season this year as well as a rapid increase in reported cases, raising concerns for strains on essential services.
University of Sydney Faculty of Medicine and Health Professor Elizabeth Elliott said there was no doubt "chaos" would be caused by the emergence of new variants in the winter flu season.
"Hospitals are already struggling with the load. And kids are not exempt. We recommend flu and COVID vaccines for all eligible," she said.
However, Professor Turville is more optimistic that precautionary measures can help ease the pressure.
"I would say if you haven't already, go and get your third dose. Although it may not stop you getting infected, it will definitely help with disease severity," he said.
"If you've had a third dose a while ago and ATAGI (Australian Technical Advisory Group on Immunisation) recommends a fourth dose, just do it. Don't get complacent.
"The other thing is, although people don't like restrictions, it's important to be considerate and wear a mask. We don't know who has or doesn't have a good vaccine response."
