Scientists were worried about a particular variant this fall. They did not expect its offspring

The World Health Organization announced in July that it was tracking the concerning new variant, which had been identified in 10 countries, including the US, and was gaining ground against other transmissible strains of the virus like BA.5 in India.

But Centaurus is no longer a worry, Dr. Raj Rajnarayanan, assistant dean of research and associate professor at the New York Institute of Technology campus in Jonesboro, Ark., told Fortune.

Instead, one of its children, BA.2.75.2, has outcompeted it, eliminating it as a threat—but replacing it with a more formidable one.

It’s one to watch this fall, he says—for more reasons than one.

‘Extensive escape’

Among BA.2.75.2’s concerning traits: Its spike protein binds to human cells tightly—better than any other variant so far, Rajnarayanan says. By doing so, it makes it more difficult for antibodies to successfully attack.

It’s picking up mutations that make it more similar to BA.5 and the deadly Delta variant of late 2021. And it’s just “a couple of mutations away from picking up increased transmission speed,” Rajnarayanan said.

To make matters worse, the new variant shows “extensive escape” ability, according to a new preprint paper released this week by researchers at the Imperial College in London and the Karolinska Institute in Sweden. The paper has not yet been peer reviewed but has been widely cited by experts.

The authors called the Centaurus spawn “the most neutralization-resistant variant evaluated to date,” and said it may effectively evade antibody immunity, built by vaccination and prior infection.

The variant could even escape immunity provided by the last monoclonal antibody treatment effective in currently circulating variants: Bebtelovimab.

“These are our last monoclonal antibodies,” said Rajnarayanan. “For the immunocompromised right now, having monoclonal antibodies is one of the best ways to mitigate infections.”

“If you take the tool away, it’s going to be a problem.”

A coming wave of multiple variants

Rajnarayanan and others, like the Institute for Health Metrics and Evaluation at the University of Washington, foresee a fall COVID wave in the US that begins to rise in late October, and peaks in late December or January.

Rajnarayanan thinks it could be fueled by multiple variants, with BA.2.75.2 likely included.

He encourages all Americans to get boosted, saying the new Omicron bivalent booster is the best tool society has against the virus.

And he shared a bit of good news: While new variants may be “immune evasive,” they won’t evade all of the body’s immune system.

Such variants dodge antibody immunity, produced by B cells. But those cells only comprise half of the immune system. T cells, which comprise the other half, can’t stop infection but can dramatically reduce the severity of it.

Immune-evading variants currently don’t touch those.

“When someone says ‘immune escape,’ it doesn’t mean it’s going to escape everything,” he said.