Evolving omicron is now a year old

On Nov. 26, 2021, the World Health Organization announced that a concerning new variant of the coronavirus, known as omicron, had been discovered in southern Africa. It soon swept to dominance across the world, causing a record-breaking surge in cases.

Now, a year later, omicron still has biologists scrambling to keep up with its surprising evolutionary turns. The variant is rapidly gaining mutations. But rather than a single lineage, it has exploded into hundreds, each with resistance to our immune defenses and its own alphanumeric name, like XBB, BQ.1.1 and CH.1.

“It’s hard to remember what is what,” said Jesse Bloom, a virus expert at the Fred Hutchinson Cancer Center in Seattle.

But unless some radically different variant emerges, Bloom predicted, this confusing jumble of subvariants will endure, making it more challenging for scientists to plan new vaccines and treatments.

“It’s always going to kind of be like it is now,” he said. “There’s always going to be some soup of new variants out there.”

When omicron emerged last November, it carried more than 50 mutations that set it apart from other variants of the coronavirus.

Most antibodies stick to the “spike” proteins on the surface of coronaviruses, blocking them from entering our cells. But some of omicron’s mutations changed parts of the spike protein so that some of the most potent antibodies could no longer stick to it.

As omicron multiplied, it continued to mutate. New versions emerged, but for the first few months, they replaced one another like a series of waves crashing on a beach. The first version, BA.1, was replaced by BA.2, then BA.5, both of which evaded some antibodies produced from earlier omicron infections.

Now, the new mutations are building up quickly, most likely because they are providing the viruses with a big evolutionary edge. In the first year of the pandemic, most people who were infected had no antibodies for COVID. Now most people do. So viruses that have extra resistance to antibodies easily outcompete others lacking it.

“The evolution that’s happening is the fastest rate it has been up to this point,” said Sergei Pond, a virus expert at Temple University in Philadelphia.

A single subvariant is not gaining all of the new mutations, however. Ben Murrell, a computational biologist at the Karolinska Institute in Stockholm, and his colleagues are tracking more than 180 omicron subvariants that have independently gained mutations causing them to grow faster than BA.5.

The competition taking place in the subvariant swarm may be preventing one of them from taking over, at least for now. In the United States, the oncedominant BA.5 now accounts for just 19 percent of new cases. Its descendant BQ.1 has risen to 28 percent. And B.Q.1.1, a descendant of B.Q.1, is the cause of 29 percent. Thirteen other omicron subvariants make up the rest.

Fortunately, the new subvariants don’t seem to be deadlier than earlier forms of omicron.