Yet another subvariant of the highly transmissible Omicron strain of Covid-19 has been detected in Australia.
The new subvariant, which is still not fully identified but is believed to be either BA.4 or BA.5, is currently under investigation by the World Health Organisation (WHO).
Victorian health authorities warned that wastewater testing from Melbourne's Tullamarine sewage catchment had found traces of the mutant virus.
This subvariant has also been recorded in South Africa, Botswana, Belgium, Denmark, the UK and Germany.
At the moment, there is no evidence to suggest it is more contagious than other Omicron subvariants already rampant in the community.
"There are currently no known significant epidemiological differences observed between the new strain and the BA.2 strain," the health department said in a statement on Friday.
The BA.2 strain, also known as "stealth Omicron", first appeared earlier this year and since then has led to a huge uptick in cases around the world including Australia.
Little is known about both the BA.4 and BA.5 strains because fewer than 200 sequences of them have been collected, according to the WHO.
Lead WHO epidemiologist Maria Van Kerkhove said at a conference on Wednesday: "We don't detect any changes in the epidemiology of people who are infected with BA.4 or BA.5 compared to previous sub-lineages of Omicron" — a point echoed by Australia's own health authorities.
Victorian chief health officer Brett Sutton said he was "not surprised" this subvariant had finally reached Australia's shores.
"Not surprised. But not worried," he tweeted.
"The point with all the newly emergent lineages is that when they out-compete existing variants, we get upward pressure on cases and more risk of getting infected.
"So get up-to-date with vaccines; wear a quality mask indoors and test when required."
In the past 24 hours, NSW has recorded 13,601 new cases, Victoria 9559, Queensland 5878, Tasmania 1334 and the Northern Territory 391.
Western Australia and South Australia have not yet released their most updated results.
It comes just a day after another Omicron subvariant — the XE strain — was first detected in another Australian state.
NSW Health authorities reported in their weekly Covid-19 surveillance report that the case of XE was detected in a recently returned overseas traveller last week.
The XE variant is believed to be 10 per cent more contagious than the original Omicron.
"This is the first XE sequence to be identified in NSW and was identified in a recently returned traveller," NSW Health said in the report.
"Another recombinant BA.1/BA.2 sequence has previously been identified but it was not of the XE lineage."
Omicron XE is a recombinant virus, which is when two separate virus strains merge to form a new, single and hybrid strain.
In Omicron XE's case, it is a combination of the two Omicron Covid variants BA.1 and BA.2.
BA.1 is the original Omicron, without any mutations.
Then there's BA.2 — or "stealth Omicron" — which has become the most dominant Covid strain in Australia.
Omicron XE was first detected in the United Kingdom on January 19, with more than 1000 cases recorded there since then.
But this is not the first time recombinant Covid viruses have been detected in Australia.
Just last week Australia's first case of "Deltacron" (a mix of Delta and Omicron BA.1) was announced in NSW, with it being detected in Queensland a day later.