The BA.2 subvariant has become the dominant strain of COVID-19 in Denmark and South Africa over the last month, with initial studies indicating it could spread between 25 to 33 per cent faster than the BA.1 strain of Omicron.
The latest genomic sampling from SA Health shows around 19 per cent of cases in South Australia are the BA.2 subvariant.
“Omicron is the dominant variant of COVID-19 in South Australia and genomic sequencing shows cases of the BA.2 subvariant are on the rise,” an SA Health spokesperson said.
“Our experience with this subvariant is still being monitored, but to date suggests BA.2 is probably more transmissible than BA.1.
“There is not enough information yet to comment on its severity.”
BA.2’s emergence comes amid a case spike in South Australia, with new infections growing from 1577 on Monday to 2560 on Wednesday and 2590 on Thursday – the highest numbers since January 21. Hospitalisations numbers, however, remain steady at less than 100.
Another 2,590 cases for South Australia and 4 deaths. The Reff is steady at 1.11. There are 91 people in hospital (up 1) and 11 in ICU (down 4). pic.twitter.com/bTjYmqWbei
— Professor Adrian Esterman (@profesterman) March 10, 2022
It also comes after a warning from New South Wales Health Minister Brad Hazzard that BA.2 could “more than double” the number of daily infections over the next month to six weeks. NSW recorded 16,288 new cases yesterday.
University of South Australia epidemiologist and biostatistician Professor Adrian Esterman said it was inevitable that BA.2 would become the dominant COVID-19 strain in South Australia.
“It’s happening already,” he said.
If BA.2 takes off – and it will do – then we’re looking at a doubling of case numbers in seven days.
Asked whether Hazzard’s gloomy forecasts applied to South Australia, Esterman said: “absolutely.”
“And that’s even just with keeping public health measures as they are, that’s not [calculating] taking them off,” he said.
Police commissioner and state emergency coordinator Grant Stevens yesterday signed off on a raft of eased COVID-19 restrictions, scrapping all limits on hospitality and home gatherings and lifting a ban on singing and dancing in public venues.
But Stevens said the new BA.2 subvariant did not factor into discussions at the COVID-ready committee where that decision was made.
“It wasn’t brought up yesterday, I’ve had no specific advice from SA Health regarding any subvariant,” he told ABC Radio this morning.
“There has been some loose reference to it but it hasn’t been brought to my attention as a variant of concern, or any indication that the arrival of this subvariant is going to change our current situation in terms of how we’re managing COVID.
“As a contrast, when Omicron first emerged there were urgent discussions and meetings held about the possible implications … we have not had that at this point in time.”
But Esterman said BA.2 is “about 1.4 times more transmissible” than the first Omicron strain, meaning COVID-19 is now “approaching the most contagious disease we know”.
The former World Health Organisation epidemiologist said BA.2 could increase South Australia’s effective reproduction number – a measure of how many infections stem from one case – to 1.5.
“At the moment in South Australia, the effective reproduction number is 1.1 as of yesterday,” he said.
“The doubling time for that is 26 days. In other words, if it stays at that, in 26 days’ time we’ll see double the number of cases we’re seeing now.
“If you multiply that by 1.4, that gets us to [an effective reproduction number] of about 1.5, so if you look at the doubling time for 1.5 – it comes down to seven days.
“In other words, if BA.2 takes off – and it will do – then we’re looking at a doubling of case numbers in seven days.”
Esterman, however, emphasised that there’s no evidence BA.2 is more lethal than BA.1 and the two strains appear to have the same ability to evade the immune system.
Premier Steven Marshall today said “any new variant is of concern” but emphasised that “it is very early days”.
“We have a national cabinet meeting this afternoon, so we’ll hear from [chief medical officer] Professor Paul Kelly,” he told reporters today.
“There is some information that would suggest this variant has higher transmissibility, but there’s no evidence to suggest there’s a higher severity.”
Marshall said the recent increase in cases is “probably logical” given the full return of students to school. The Premier predicted that case numbers are “probably going to remain around that number that they’ve been at for the last week or so”.
“Hospitalisation is going down in South Australia and that’s the primary metric in South Australia that we’re concerned about,” he said.
“The continued lower numbers of hospitalisation has really led us to be in a wonderful position to further ease those restrictions as of one minute past midnight tonight.”
Omicron BA.2 is about 1.4 times more infectious than BA.1. The basic reproduction number (R0) for BA.1 is about 8.2, making R0 for BA.2 about 12. This makes it pretty close to measles, the most contagious disease we know about.
— Professor Adrian Esterman (@profesterman) March 10, 2022
South Australia’s COVID-Ready committee will meet next week to determine whether to reduce the quarantine period for close contacts of positive cases down from the current 14 days.
The meeting comes just a week before the state election and is the only time this year a restrictions lift has been foreshadowed to occur on a non-fortnightly basis.
Esterman said there could be long-term consequences for easing restrictions too early.
“In South Australia we’re getting 2500 cases a day, the Government says it doesn’t matter because we’re not seeing hospitalisations going up – and that’s true – but what they don’t mention is that since the 1st of January we’ve had 150,000 cases,” he said.
“If only five per cent of them end up with long-term health problems because of COVID – it’s probably more like 10 per cent or higher – you’re getting thousands of people with long term health problems, which the Government forget about, they don’t mention it.
“No matter what the Government says about relaxing public health measures, I’d recommend people to keep wearing face masks and to still take precautions, especially if you’ve got underlying health problems or you’re elderly.”
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