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Since Omicron swept across the globe in 2021, the evolution of SARS-CoV-2 has moved at a slower and more predictable pace. New variants of interest have come and gone, but none have matched Omicron’s 30-odd mutations or its ferocious growth. Then, about two weeks ago, a variant descended from BA.2 popped up with 34 mutations in its spike protein—a leap in viral evolution that sure looked a lot like Omicron. The question became: Could it also spread as quickly and as widely as Omicron?
This new variant, dubbed BA.2.86, has now been detected in at least 15 cases across six countries, including Israel, Denmark, South Africa, and the United States. This is a trickle of new cases, not a flood, which is somewhat reassuring. But with COVID surveillance no longer a priority, the world’s labs are also sequencing about 1 percent of what they were two years ago, says Thomas Peacock, a virologist at the Pirbright Institute. The less surveillance scientists are doing, the more places a variant could spread out of sight, and the longer it will take to understand BA.2.86’s potential.
Peacock told me that he will be closely tracking the data from Denmark in the next week or two. The country still has relatively robust SARS-CoV-2 sequencing, and because it has already detected BA.2.86, we can now watch the numbers rise—or not—in real time. Until the future of BA.2.86 becomes clear, three scenarios are still possible.
The worst but also least likely scenario is another Omicron-like surge around the world. BA.2.86 just doesn’t seem to be growing as explosively. “If it had been very fast, we probably would have known by now,” Peacock said, noting that, in contrast, Omicron’s rapid growth took just three or four days to become obvious.
Scientists aren’t totally willing to go on record ruling out Omicron redux yet, if only because patchy viral surveillance means no one has a complete global picture. Back in 2021, South Africa noticed that Omicron was driving a big COVID wave, which allowed its scientists to warn the rest of the world. But if BA.2.86 is now causing a wave in a region that isn’t sequencing viruses or even testing very much, no one would know.
Even in this scenario, though, our collective immunity will be a buffer against the virus. BA.2.86 looks on paper to have Omicron-like abilities to cause reinfection, according to a preliminary analysis of its mutations by Jesse Bloom, a virologist at the Fred Hutchinson Cancer Center, in Washington, but he adds that there’s a big difference between 2021 and now. “At the time of the Omicron wave, there were still a lot of people out there that had never been either vaccinated or infected with SARS-CoV-2, and those people were sort of especially easy targets,” he told me. “Now the vast, vast majority of people in the world have either been infected or vaccinated with SARS-CoV-2—or are often both infected and vaccinated multiple times. So that means I think any variant is going to have a very hard time spreading as well as Omicron.”
A second and more likely possibility is that BA.2.86 ends up like the other post-Omicron variants: transmissible enough to edge out a previous variant, but not transmissible enough to cause a big new surge. Since the original Omicron variant, or BA.1, took over, the U.S. has successively cycled through BA.2, BA.2.12.1, BA.5, BQ.1, XBB.1.5—and if these jumbles of numbers and letters seem only faintly familiar, it’s because they never reached the same levels of notoriety as the original. Vaccine makers track them to keep COVID shots up to date, but the World Health Organization hasn’t deemed any worthy of a new Greek letter.
If BA.2.86 continues to circulate, though, it could pick up mutations that give it new advantages. In fact, XBB.1.5, which rose to dominance earlier this year, leveled up this way. When XBB.1.5’s predecessor was first identified in Singapore, Peacock said, it wasn’t a very successful variant: Its spike protein bound weakly to receptors in human cells. Then it acquired an additional mutation in its spike protein that compensated for the loss of binding, and it turned into the later-dominant XBB.1.5. Descendents of BA.2.86 could eventually become more transmissible than the variant looks right now.
A third scenario is that BA.2.86 just fizzles out and goes away. Scientists now believe that highly mutated variants such as BA.2.86 are probably products of chronic infections in immunocompromised patients. In these infections, the virus remains in the body for a long time, trying out new ways to evade the immune system. It might end up with mutations that make its spike protein less recognizable to antibodies, but those same mutations could also render the spike protein less functional and therefore the virus less good at transmitting from person to person.
“Variants like that have been identified over the last few years,” Bloom said. “Often there’s one sample found, and that’s it. Or multiple samples all found in the same place.” BA.2.86 is transmissible enough to be found multiple times in multiple places, but whether it can overtake existing variants is unclear. To do so, BA.2.86 needs to escape antibodies while also preserving its inherent transmissibility. Otherwise, Bloom said, cases might crop up here and there, but the variant never really takes off. In other words, the BA.2.86 situation basically stays where it is right now.
The next few weeks will reveal which of these futures we’re living in. If the number of BA.2.86 cases starts to go up, in a way that requires more attention, we’ll know soon. But each week that the variant’s spread does not jump dramatically, the less likely BA.2.86 is to end up a variant of actual concern.
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Sarah Zhang
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