An Omicron sub-variant of COVID-19 that can evade vaccine immunity is on the rise in Victoria, with health authorities warning it is on track to be the state's major strain in line with virus spread in NSW and Queensland.
Traces of the BA.4/BA.5 strain in Victoria's metro and regional wastewater "have risen significantly in recent weeks, indicating increasing transmission of this sub-lineage in the community," Victoria's Chief Health Officer Brett Sutton said in a statement on Saturday.
Mr Sutton said the BA.4/BA.5 sub-lineage – first identified in catchments in April – accounted for 17 per cent of Victorian infections and was forecast in coming weeks to overtake BA.2 to become the state's dominant strain.
He said the strain's lifting numbers in Victoria followed similar patterns in NSW and Queensland.
"The Department of Health anticipates the prevalence of BA.4/BA.5 in Victoria is likely to result in an increase in cases, including reinfections, and hospital admissions," he said.
"This is because the strain has a greater ability than BA.2 to evade immunity provided by vaccination and earlier COVID-19 infection."
There was no evidence at this stage that the sub-variant causes more severe disease, but authorities were "closely monitoring the situation".
Doctor pleads for people to stay home if sick
Medical experts this week renewed calls for people to get their booster in the wake of rising infections and hospitalisations as new sub-variants emerge during winter.
On Saturday, more than 28,000 new cases and 56 deaths were recorded nationwide in the latest reporting period. There were almost 225,000 active cases across the country, with 3046 patients in hospital care.
As case numbers rise, doctors have urged those with symptoms to stay home and get tested, especially in the wake of easing vaccine and mask mandates in some parts of the country.
Several states have started to unwind restrictions including allowing unvaccinated school staff back to work, lifting bans on unvaccinated visitors at nursing homes or relaxing mask requirements at airports.
"We've seen too many people who have symptoms who are going around in the community who perhaps have had a negative (Rapid Antigen Test) saying, 'Oh, it's not COVID, it's not the flu. I'm okay to be around people'," Australian Medical Association Queensland president Maria Boulton said on Saturday.
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