Forget about a single strain: The new COVID calculus is all about viral families

The transfer of power used to be relatively straightforward from variant to variant, from the original strain, to Alpha, to Delta, to Omicron—one washing over the world before another took over.

Now it’s a battle royal between prominent viral “families” warring to keep power within the lineage. No single family—BA.5, XBB, nor BQ—has achieved global success this fall. Not yet, at least.

As the virus behind COVID—namely the Omicron variety—mutates at an unprecedented rate, the focus of scientists has shifted from single strains to related groups of them.

Case in point: XBB, a combination of two different Omicron spawns that began surging in Singapore and Bangladesh in recent weeks. It has yet to arrive in the U.S., at least officially. But its grandchildren, XBB.1.1 and XBB.1.3, have, according to data from GISAID, an international research organization that tracks changes in COVID and the flu virus.

These days, it’s risky to look at one country and assume that because it’s experiencing a certain wave, another country will soon experience the same, Ryan Gregory, a professor of evolutionary biology at the University of Guelph in Ontario, Canada, told Fortune.

“The XBB [surge] Singapore sees may not be the one we see in the U.S.,” he said. 

The summer that changed everything

As far as viral evolution goes, all was relatively simple through the “stealth Omicron” surge earlier this year, experts say. A new variant would materialize and the number of cases would surge, vacillate a bit, then fall, like clockwork.

But the calculus changed this summer with BA.5. The new-generation Omicron spawn surged globally—then surged again in some places like Germany and France. Meanwhile, in other countries, fellow Omicron strains XBB or BQ—or their descendants—began to swell.

Today, there are hundreds of Omicron strains, all with mutations that provide increased transmissibility, the ability to escape immunity, the potential to cause more severe disease, or a combination thereof.

The scene differs depending on where you are. BA.5 variants are still dominant in the U.S., according to GISAID data, while infections involving BQ variants are also rising.

France’s largest proportion of cases are also BA.5 family members. But the strains that are dominant there differ slightly from those that are most common in the U.S.

In Chile, “stealth Omicron” is still going strong, making up nearly 44% of cases, with descendants of itself and the original Omicron on its heels. And oft-locked-down China is a different world altogether, with one of the original COVID strains accounting for 31% of cases, followed by Delta at nearly 19%.

The story of COVID is no longer “one variant rising, doing its thing, we mitigate again, it comes back down, we brace for the next one,” Gregory said. “Things are coexisting at the same time, moving around. The longer they circulate, the more you get combinations.”

Not only are multiple viral families warring it out, with different levels of success in different regions, but battles are occurring within families. In effect, relatives are fighting among themselves to lead lineages, Gregory says.

Victories in turn?

The extremely immune evasive BQ family will almost certainly become dominant in the U.S. in the coming weeks, according to multiple experts. But that doesn’t mean the U.S.—or any other country with rising levels of BQ—has dodged the other variants.

XBB will likely fuel the following U.S. wave, then perhaps XBC, a Delta-Omicron hybrid, Gregory and Raj Rajnarayanan, assistant dean of research and associate professor at the New York Institute of Technology campus in Jonesboro, Ark., tell Fortune.

That could mean the U.S.—and other countries—are in for a winter during which multiple viral families are briefly dominant before receding. There may not be one COVID peak in late 2022, but overlapping surges fueled by different variants that create a wide “ugly peak” with a jagged top, Rajnarayanan says.

Prior to this summer’s BA.5 surge, COVID was in a constant “predator-prey cycle,” according to Gregory.

Those days are gone.

“It’s an ecology now,” Gregory said. “It was, ‘How many rabbits and how many wolves?’ Now, it’s a whole ecosystem.”