A researcher in Cyprus identified a COVID-19 variant that had features of both the deadly Delta and the highly transmissible, immune-evasive Omicron variants. “Deltacron,” as the new variant became known, was a bit of a “frankenvirus” that combined the two strains.

Deltacron failed to take off, and it soon disappeared. A second Delta-Omicron hybrid later arose then also subsided. 

But the phenomenon that caused it is likely to come into play this fall. Scientists expect a sizable wave of COVID cases October through January, fueled by multiple Omicron spinoffs that look increasingly alike—both to each other and to older versions of the scourge.

They’re expected to be the most immune-evasive, transmissible versions of the virus yet. Their similarity could be a blessing or curse: It could make them easier to fight—or harder to control.

As Omicron evolves, it’s “rediscovering solutions that have been used before” in variants like Alpha, Gamma, and Delta “while bringing some new things along with its lineage,” Dr. Stuart Ray, vice chair of medicine for data integrity and analytics at Johns Hopkins Department of Medicine, told Fortune.

“It’s a fascinating part of evolution,” he said. “We see the same scraps of cloth being used to make a new quilt.”

Different paths, same goal

While a fall wave of COVID may be fueled by multiple variants—as many as five or more—the differences between them could be minor, Dr. Raj Rajnarayanan, assistant dean of research and associate professor at the New York Institute of Technology campus in Jonesboro, Ark., told Fortune.

In a form of parallel evolution called convergent evolution, variants are collecting identical sets of concerning mutations. In other words, multiple strains of the same virus are picking up similar mutations, like ones that will help them evade immunity and make it easier for the virus to spread, according to Rajnarayanan.

One example: The wave of globally dominant BA.5 is beginning to recede in many locations—but its spin-offs are picking up mutations that promote immune evasion, Dr. Michael Osterholm, director of the University of Minnesota’s Center for Infectious Disease Research and Policy (CIDRAP), told Fortune.

“We’ve not seen this type of immune evasion before,” he said, speaking of the variants’ increasing ability to dodge the immune system and tools that bolster it, like vaccines and treatments.

Meanwhile, COVID strains are also mutating through a process called recombination—the same strategy the so-called Deltacron strain used. In this scenario, two variants meld into one. Case in point: new variant XBB, a merger of two different Omicron spawns that is the most immune-evasive COVID strain seen yet, according to Rajnarayanan.

Unlike the initial Deltacron—which was only identified in a single lab, signaling that it may have been a product of lab contamination—XBB is being found worldwide in places like Bangladesh, Israel, Singapore, Germany, and Denmark, he said.

With all the mixing and matching of Omicron spawn occurring this fall, will the resulting muddled mess constitute some kind of “super virus”?

It’s impossible to know, experts say. But Omicron may be close to reaching a “local fitness peak,” meaning the variant—while still evolving quickly—might soon be unable to spread or evade human immune systems any better than their predecessors. 

“I do wonder if it’s running out of options,” Ray said of Omicron. “It doesn’t mean it’s reached the peak of spread, but it may put some bounds on it.”

A new foe this winter?

If Omicron is indeed peaking in terms of performance, it could pave the way for the entrance of a completely new variant, like Delta, which arrived in the U.S. in the summer of 2021, and Omicron, which hit several months later.

“Somewhere there might be a Pi lurking that has a new set of solutions,” Ray said, referring to the possibility of another major variant along the lines of Alpha, Beta, Gamma, Delta, and Omicron. “If the virus runs out of space for advantageous changes, a new variant might emerge that changes the calculus for all of us.”

He continued: “It’s been a while since we’ve seen a big new variant come out of left field. But I think it’s reasonable to believe it’s going to happen this winter. It’s just nothing anyone can predict.”

Osterholm agrees that the world “could be in a situation where Pi or Sigma show up.”

“None of us know—that’s the challenge right now,” he said. “We just have to be very humble and say we don’t know what the next shoe to drop is.”

It’s also possible that “we begin to see what I call a ‘soft landing,’” a gradual lowering in the number of cases, he added.

Osterholm sees no evidence, however, that COVID is turning into a seasonal virus like the flu and that one vaccine a year will suffice, like some White House officials recently suggested.

The virus, he says, is a “three act play.”

“I think we’re only in the second act,” he said. “That’s the problem.”