Omicron COVID strain takes over in Australia, but experts say Delta is still circulating and boosters are critical – ABC News

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Omicron has taken over as the most prevalent coronavirus variant in Australia, but experts say the true scope of infections — and the continued spread of Delta — is still unknown as authorities become overwhelmed with case numbers.
The introduction of self-reporting for rapid antigen test results last week, delays in PCR testing and record case numbers over the holiday period mean genomic sequencers — the experts who analyse COVID-positive strains — have been battling to keep up.
It also means experts modelling a peak in case numbers across Australia has become harder to predict.  
On Wednesday, NSW Chief Health Officer Kerry Chant said about "90 per cent" of all cases in the state have been infected with the Omicron variant.  
She said of the patients in ICU in NSW, about 67 per cent have the Omicron strain, with the remaining 33 per cent infected with Delta.
One independent data analyst suggests Omicron, which was first transmitted in Australia on December 3, is now making up more than 90 per cent of infections across Australia. 
Authorities have been closely watching the rising hospitalisation rates across the country, and although Omicron is widely considered to be a milder version of the virus compared to the Delta strain, the World Health Organization has warned it is not a "mild" disease.
NSW Chief Health Officer Kerry Chant said this week she knew of at least one "young person" who died after contracting the Omicron strain.
She said genomic sequencers were working to confirm which variants were involved in the deaths and hospitalisations of COVID patients.
In Victoria, although the state has introduced mandatory reporting of positive RAT results, genomic sequencing of the variants is not as clear.   
Victorian Premier Dan Andrews said on Tuesday the breakdown of Omicron and Delta circulating in the state would be something he'd "come back to" later in the week after speaking to the state's health authorities.
Queensland Chief Health Officer John Gerrard said his state, which opened up in mid-December, was seeing a "95 per cent" prevalence of Omicron.
Virologist Tony Cunningham, from Sydney's Westmead Institute, said there was no doubt Omicron had become the dominant strain across the country, but Delta was still "out there".
However, he said it was impossible to know the exact numbers because of the self-reporting of positive RAT results — not yet available in NSW — and the delays over the Christmas period.   
"We don't have enough tests to give us totally accurate figures," he said.
"And this is one of the problems we have with RATs."
Melbourne-based data integration specialist Mike Honey has been analysing data provided to online platform GISAID — which collects genomic sequencing of the virus from across the world — and the Australian-based Communicative Diseases Genomic Network.
After "scraping" the data trends over the past two months, he calculates Omicron now makes up more than 90 per cent of all infections Australia-wide.
According to the data, Omicron, overtook Delta as the most prevalent strain in Australia about midway through December — after just two weeks of circulation in the community.    
This week the World Health Organization said it believed Delta was still the more common strain worldwide, as a record 9.5 million cases of COVID were tallied across the globe — "the highest number" reported so far in the pandemic.  
According to GISAID, Omicron is yet to take over in some European countries, with Germany (18.3 per cent Omicron), France (48.6 per cent), Italy (38.5 per cent) and the Netherlands (30.7 per cent), reporting numbers lower than 50 per cent. 
However, Omicron is now responsible for 80 per cent of infections in the UK, 65 per cent of US infections, 90 per cent in Japan and 100 per cent of all infections in South Africa.
While the infectious Omicron variant of COVID-19 appears to produce a less severe disease than the globally dominant Delta strain, it should not be categorised as "mild", World Health Organization officials say.
Professor Cunningham said Omicron was clearly supplanting Delta as the key variant across the world.
But he said it was too early to predict when case numbers in Australia would peak, particularly with the different states opening up at different times and the delays in testing results.    
In NSW, the first Australian state to open up, health authorities are predicting cases to peak by the middle of this month and subside by mid-February. Experts predict Victoria to follow, with a peak later this month.   
"We're seeing huge numbers [of Omicron] in the UK, US, Europe and South Africa," he said. "But interestingly in South Africa it's peaking, and in the UK there's some evidence it might be peaking.
"That might give us an indication of what will happen here.
"But clearly we're still in the expansion phase with Omicron, and you'd have to be a brave person to predict when the peak will occur in Australia.  
"It's clearly much more transmissible than Delta, and we've seen it can evade two-dose vaccines. So it's critical that we encourage as many people as possible to get a booster to ensure we are protected."   
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