ABOVE: Artist’s rendition of BA.2.75 © ISTOCK.COM, UDOMKARN CHITKUL

The Omicron subvariant BA.2.75, also dubbed Centaurus—seemingly because some guy on Twitter decided it should be—continues to drive up the number of COVID-19 cases in India, where it was first detected in May.

There, the subvariant seems to have some sort of competitive advantage over BA.5, the subvariant largely responsible for the latest ongoing wave of coronavirus infections around the world, Catholic University of Leuven evolutionary biologist Tom Wenseleers tells Nature. The BA.2.75 subvariant has also made its way to over 20 other countries, including several in the Americas and Europe. Still, experts are mixed on how much of a threat it will pose to the rest of the world amidst and in the wake of the BA.5 surge, the outlet reports.

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“It’s clearly growing pretty well in India, but India hasn’t got much BA.5, and it is still very unclear how well it fares against [that],” Tom Peacock, a virologist at Imperial College London, told The Guardian last month.

Like other Omicron subvariants, BA.2.75 is more infectious and better at evading the human immune system—both vaccine- and infection-induced protections alike—than earlier variants of concern. Though data are still limited, researchers have determined that the subvariant carries nine mutations on its spike proteins. “That’s the part of the virus that sticks out and binds to the host cell receptor, and those mutations allow the virus to bind to that receptor more efficiently,” Matthew Binnicker, director of the Clinical Virology Laboratory at the Mayo Clinic, explains in a press release.

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Experts are reluctant to sound the alarm, however, as the wave of BA.5 infections may reduce the number or severity of cases attributed to BA.2.75. Both subvariants seem to have descended from the earlier Omicron subvariant BA.2, and thus their genetic similarities may leave the immune system primed to fend off one after defeating an infection of the other.

A phylogenetic tree of the major SARS-CoV-2 variants and subvariants illustrating the close relationship between Centaurus, or BA.2.75, and BA.5.
Omicron subvariants BA.5 and BA.2.75 are closely related, raising the possibility that the immune response to an infection of one may prevent someone from catching the other.

This seems borne out by the low rates of BA.2.75 cases in countries to which it has spread that have already experienced or are currently experiencing a surge of BA.5 infections. “We’re coming to a point where these variants are sort of competing with each other and they’re almost equivalent,” Shahid Jameel, a University of Oxford virologist who led India’s coronavirus sequencing efforts, tells Nature. “I think people who have had BA.5 will not have a breakthrough [infection] with BA.2.75, and vice versa.”

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Meanwhile, the BA.2.75 surge in India may potentially stem from greater local protections against BA.5, which could exist because the variant shares mutations with the Delta variant that exploded in the country in 2021, Nature reports, though that and other explanations for the subvariant’s disparate spread remain speculative until more data roll in.

As the BA.5 wave ends and protections against the subvariant eventually fade away, it’s unclear what will take its place as the dominant strain of SARS-CoV-2, experts tell Nature. It’s possible that an even newer subvariant, BA.4.6, which is currently spreading in Europe and North America, will outcompete BA 2.75 to succeed BA.5, or that the two subvariants will each become a problem in different countries, Nature reports.