Omicron's sister: how dangerous is the new subvariant BA.2?

The Omicron offshoot has been detected in more than 50 countries, including Britain, the United States, Israel, India, Singapore, the Philippines, Denmark and, over the past week, Australia, where 22 cases have been sequenced.

Based on preliminary data, the general consensus among experts is that it's too soon to conclude BA.2 is more or less dangerous than previous variants.

Some experts, however, say the very fact this latest iteration of COVID-19 is unquestionably more infectious spells problems for vulnerable populations and our health system, which is already under unprecedented strain.

What is the BA.2 variant?

The BA.2 sub-variant has, in some quarters, ominously been christened the "son" or "daughter" of Omicron, but experts, including Burnet Institute epidemiologist Mike Toole, have said neither description is particularly apt.

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Health officials first noticed BA.2 shortly after they discovered BA.1, which happens to be the Omicron subvariant currently responsible for 98 per cent of COVID-19 cases globally.

Notably, both BA.1 and BA.2 are offshoots of the "mother" Omicron strain (BA1.1), itself an offshoot of the original ancestral strain that kicked-started all of this misery.

So, viewed from that perspective, BA.2 might better be understood as the "sister" of BA.1, as both variants evolved from the same genetic branch of COVID-19 known as Omicron.

Why has it been nicknamed the "stealth" variant?

Genetically, BA.1 and BA.2 share a great deal in common, but there are some significant differences between their spike proteins.

"One of those differences," Professor Toole said, "is that BA.2 does not have the spike-gene deletion that [BA.1] has."

"The missing S-gene in [BA.1] made it easy to identify or recognise in a PCR test, so you didn't need to do genomic sequencing on thousands of people to know it was spreading."

This means BA.2 is only being detected in countries that are undertaking extensive genomic sequencing. Given most countries remain overwhelmed with cases at the moment, nobody really knows how long the subvariant has quietly been spreading - hence its "stealthy" nature.

Is it more transmissible?

Emerging data from Denmark, where BA.2 accounts for 80 per cent of cases, suggests the subvariant is at least 1.5 times more transmissible than the original Omicron.

The study found the new subvariant had an overall growth advantage over the original Omicron subvariant (BA.1) of around 10 per cent. By contrast, the original Omicron subvariant had a four per cent growth advantage over Delta, itself three times more contagious than the Wuhan strain.

Professor Toole said the new subvariant's sheer transmissibility has led to speculation it would prompt yet another wave of infections across the globe.

"If it's 1.5 times more transmissible, that means one infected person will spread the virus to 50 per cent more people than they would have with [the BA.1 Omicron subvariant]," he said.

"So, the virus appears to becoming fitter, but what we don't know yet is whether it's intrinsically more transmissible, in that it's a direct cause of the mutation, or whether its increased transmissibility is a result of greater immune escape."

How will our vaccines hold up?

The short answer is nobody yet knows for certain whether BA.2 is vaccine resistant. However, a preliminary study released by the UK Health Security Agency (UKHSA) last weekend suggested protection against hospitalisation waned to between 70 and 80 per cent ten weeks after a booster shot.

Bearing in mind protection against severe disease with Delta sat around 96 per cent, the early signs aren't encouraging.

In more bad news, BA.2 has infected people in Denmark who previously had BA.1, suggesting prior Omicron infection affords little in the way of natural immunity.

Is BA.2 more virulent?

At this stage, this is one of the big unknowns. There's no sign yet that BA.2 causes more severe disease than BA.1 or vice versa.

Will its impact on hospitals be severe?

Whether or not BA.2 is more toothy or deadly than its sister remains to be seen, but its growth advantage alone means it probably will renew pressure on the health system, placing it under severe stress.

But its overall impact on the health system, Professor Toole said, would turn on the extent to which government has invested in evidence-based strategies that reduce transmission.

"Pandemic complacency is always our biggest threat," he said. "BA.2 is a reminder that we need to be ready and have a clear plan to respond to any new variant that emerges."

"This plan needs to prepare us for new variants that are more transmissible or virulent or both."

The defining feature of any suppression strategy, he said, must focus on ventilation, with the introduction of air purifiers and Co2 filters in nursing homes, hospitals, schools and hospitality mandatory.

"We eliminated cholera from the western world by providing cleaner water and sanitation," he said.

"There's no reason we couldn't achieve the same with a respiratory disease like COVID-19 if we more thoroughly addressed ventilation issues, which have never been taken seriously by government.

"There's about 30000 proteins in the virus and any one of them could mutate in a new combination that makes [the virus] fitter. So, we should never be surprised when new variants emerge, because it's inevitable."

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