As the Omicron COVID-19 variant continues its dominance across the world, subvariants are emerging and making their way into Australia. But how worried should we be?
Associate Professor Stuart Turville from the Kirby Institute at UNSW has been researching Omicron since it was first detected in late 2021. He told the AusSMC that variants emerge as a result of small changes which can have big impacts on the way the virus spreads.
"Two viruses dominated in 2021 and they were Delta and to a lesser extent Lambda. They have small changes that made the virus more transmissible and to a certain degree could reduce the potency of an antibody response by roughly 2 fold," A/Prof Turville said.
He said the arrival of Omicron BA1 and BA2 changed that dynamic. Compared to Delta, both these variants have a far greater ability to evade a previous antibody response, whether from vaccination or prior infection.
"Compared to the modest 2 fold drop in potency observed by Delta, these new variants resulted in a greater than 16 fold drop," he said.
A/Prof Turville said subvariants currently emerging such as BA4, BA5 and BA2.12.1 have all come from BA2, which appears to have won the race to become the dominant variant right now.
He said some of the changes seen in these new subvariants were also found in other, pre-Omicron variants like Lambda, which was never dominant in Australia, and Delta, which we know to be more transmissible and vaccine-evasive than earlier variants.
"BA4, BA5 and BA2.12.1, are examples of small changes in the right places. BA2 sublineages are 'whittling away' and are likely becoming fitter in the real world and displacing the original BA1 and BA2," A/Prof Turville said.
He said there were two ways variants became dominant; becoming "fitter" or more easily transmissible, or becoming more "slippery," able to get past existing antibodies people develop through getting vaccinated and/or becoming infected. The changes observed in these subvariants suggest they may become either fitter, slipperier or both, but A/Prof Turville said it would take time to be sure.
"The key thing is that these are small changes in the virus, and not unlike what we have seen before. They may not resemble the large shift we saw with Delta to Omicron," he said.
Whether any of these variants lead to more severe disease will also be important to watch, although A/Prof Turville said gathering enough data on this was a long process.
Researchers use animals to get a head start on figuring out how different variants change the severity of disease, and A/Prof Turville said animal studies of Omicron have shown it may attack the body in a different and therefore less severe way than Delta.
"[Omicron BA1 and BA2] changed the way the virus entered cells. In doing so, it meant the virus infects the upper respiratory tract far better (bronchial tissue), and the lower lung not as well. In animal models, this was observed to result in lower disease severity," he said.
A/Prof Turville said researchers would continue to test these Omicron subvariants to see if they still infect the bronchial tissue rather than the lower lung, and combine that with real-world data to keep an eye on how humans are handling the disease.
"There is still a lot about this virus that is unknown and there are many paths it has the potential to take."
You can read the full Expert Reaction here.
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