Just as Australians and other nations begin to enjoy renewed freedoms, a potentially more infectious coronavirus mutation is emerging.
A university study suggests Omicron sub-variant BA.2 is already the dominant strain in New South Wales. Photo: AFP
New South Wales Health Minister Brad Hazzard said cases could "more than double" in six weeks due to new Omicron sub-variant BA.2, as the state recorded 16,288 cases on Thursday, its highest number since January.
Across the globe, countries have experienced a surge in cases credited to BA.2, including Denmark, the UK, Norway and Sweden, according to Danish research institute Statens Serum Institut (SSI).
Should people be worried? Here's what is known so far.
What is BA.2?
Omicron has several sub-lineages, with the BA.1 variant accounting for most Omicron cases in NSW and worldwide.
But BA.2, also known as Nextstrain clade 21L, has recently become the most dominant strain in NSW, a University of New South Wales study suggests.
The two variants differ in genetic sequence, including in amino acids and proteins.
Is BA.2 more transmissible?
The World Health Organisation (WHO) says studies have shown the BA.2 variant appears to be more transmissible than BA.1.
UNSW School of Population associate professor James Wood said the new sub-variant was about 25 percent easier to catch than the original strain.
"It first became clear in Denmark it was more transmissible than Omicron," Dr Wood said.
"The dominant variant, for about a month, has been BA.2.
"We've started to see that pattern in a number of other countries like the UK and now we're getting data that's confirming that's the case in Australia, in particular NSW.
"We think by the end of the month it will [account for more than] be 90 percent of the cases [in NSW]."
NSW deputy chief health officer Marianne Gale said for a new strain to become dominant it had to be more transmissible or be able to evade vaccines and the immune response.
"What we are seeing is a trend to an increasing rise of the BA.2 sub-lineage of Omicron," she said.
The World Health Organisation says studies have shown the BA.2 variant appears to be more transmissible than BA.1, shown at the front of this 3D rendering. Photo: 123RF
Is BA.2 more deadly?
Despite being potentially easier to catch, the WHO says infection data from South Africa, the UK and Denmark suggest there is no difference between the severity of Omicron's BA.1 and BA.2.
Dr Wood said there was "no real evidence" that it was more serious.
"Denmark hasn't experienced a surge in deaths … I'd say it's similar," he said.
"We can expect a rise in hospitalisations and intensive care … [but] we have progress in booster coverage - that's the sort of thing that will help keep severe disease down."
Dr Gale said the severity of BA.2 compared to its predecessor was still unknown.
"Experience overseas has shown us that BA.2 quite rapidly can overtake BA.1 to become the dominant type of Omicron," she said.
"Again from overseas, BA.2 has evidence of being more transmissible - it can infect people quicker.
"But we don't have evidence that it is any more or less severe clinically."
The new 'variant of concern'
Minister Hazzard said he was concerned by the emergence of BA.2.
"It's highly likely … in only another month or six weeks we could be looking at cases more than double what we're currently getting," he said.
"People need to understand that while the community has gone to sleep on the virus, the virus hasn't gone to sleep on the community."
The WHO released a statement calling it a "variant of concern", but Dr Wood said there was no need to be "overly concerned".
"Vaccines seem to work just as well against it," he said.
"We expect people who were infected with Omicron recently will have very good protection against it.
"So it's not the same kind of level of concern we had in December, when cases shot up quite rapidly and we were concerned with our health system's [ability to cope]."
How can people protect themselves?
The risk of catching Covid-19 will go up for a couple of months, Dr Wood said.
But there was no need for drastic measures like hibernating at home.
The easiest way to stay protected was to get a vaccination.
"For now, I wouldn't change your behaviour too much, but keep your eye on what's happening," Dr Wood said.
"If you're in a risk group and you haven't got a vaccine, I'd consider getting one.
"If you haven't had a booster dose, go get a booster dose - particularly if you're an older person or someone with risk factors.
"And I'd consider wearing a mask again if you're concerned of catching Covid."
Nick Talley from the University of Newcastle said booster shots were crucial to preventing serious illness.
"The risk is the people who aren't fully vaccinated could be exposed," Dr Talley said.
"I think everyone would want to forget about Covid with the war in Ukraine, the terrible floods.
"But we need to protect ourselves."
-ABC