The Department of Health recently confirmed Australia is heading into a new COVID wave, with case numbers rising across the country. This mirrors a global pattern, as new Omicron subvariants compete for the top spot as dominant strain. BQ.1 and XBB are the two most prominent of these sub-strains.
The latest uptick is the first COVID surge since our ‘winter variant’ Omicron BA.5. While fewer people are getting tested these days, the proportion of tests returning positive results is on the rise. Hospitalisations are also growing in some states.
However, what’s new about this wave is that it isn’t driven by a single dominant variant (at least, not yet). Experts have used the phrase “COVID soup” to describe the situation.“It’s no longer one big wave of a single variant being replaced by another single variant,” says medical microbiologist and infectious diseases expert, Dr Noelle Sherry, marking it as a pandemic turning point.
A similar dynamic is emerging in other countries experiencing new waves, with several subvariants in competition to become the next dominant strain.
BQ.1 and XBB are among the strongest contenders.
BQ.1 – Omicron’s grandchild
BA.2 was one of the first Omicron variants to become widespread (think UK wave earlier this year). One of its lineages, BA.2.75, is currently a primary strain in Australia and many other countries.
BA.2 can be thought of as a sort of parent Omicron strain, which produced a child in BA.5. BA.5 drove that winter surge in Australia I mentioned earlier – and remains a pretty strong strain today too.
Finally, BA.5 produced the sublineage BQ.1 – in other words, BQ.1 is kind of like the grandchild of BA.2.
BQ.1 has been circulating widely in the UK, Europe and North America. At the start of this month, it accounted for 14% of all COVID infections in the US, while its close relative BQ.1.1 accounted for 13%.
BQ.1 has numerous mutations in its spike protein, just like previous dangerous variants – you’ll recall these kinds of mutations make it easier for COVID to evade immune responses. This means vaccination and prior infection with another variant are not as effective for resisting BQ.1.
XBB – Frankenstrain
Although the government has said it is “closely monitoring” the transmission of BQ.1, it’s XBB that’s a little closer to home for Aussies. While BQ.1 roves around the northern hemisphere, XBB has been dominating waves in Asia.
58% of recent cases in Singapore have been XBB, and has governments in other Asian countries – like Japan – concerned.
Unlike BQ.1, XBB is not a direct descendant of Omicron BA.2. Instead, it’s what is known as a ‘recombinant’, born from genetic exchange between two other subvariants: BA.1.10.1 and BA.2.75. While there have been other recombinants before, XBB is the first to spread widely.
XBB also has mutations in the spike protein. Some are in the same parts as in BQ.1 – the receptor-binding domain. But it also has mutations in the ‘N-terminal domain’, a different target of antibodies, making it extra immune-evasive.
The good news is that overseas experiences seem to indicate neither strain causes more severe infection, with hospitalisations remaining relatively low. It’s important we do our best to keep hospitalisations low in Australia too, and avoid over-straining the healthcare system again.
So make sure you’re up to date with your boosters, and wear a mask in public settings as much as possible, especially with the holiday period approaching!
Cover photo by Parastoo Maleki on Unsplash.
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