Happy birthday Omicron

A year after the discovery of the variant, virologists are still struggling to keep up with Omicron's rapid evolution.

On November 26, 2021, the World Health Organization announced that a worrying new variant of the coronavirus, known as Omicron, had been discovered in Southern Africa. It quickly took over the entire world, causing a record increase in the number of cases.

Now, a year later, Omicron still has biologists scrambling to track its surprising evolutionary turns. The variant quickly gains mutations. But rather than a single lineage, it 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's what," said Jesse Bloom, a virologist at the Fred Hutchinson Cancer Center in Seattle.

But unless Unless a radically different variant emerges, Dr. Bloom predicted, this confusing jumble of sub-variants will persist, making it harder for scientists to plan new vaccines and treatments.

"This as it is now," he said. "There will always be soup of new variants."

When Omicron appeared last November, it carried over 50 mutations that set it apart from other variants of the coronavirus. Many researchers favor the idea that it emerged in a single person, possibly with a weakened immune system, who had a chronic case of Covid that lasted for months.

Last month, however, a team of scientists from the University of Minnesota suggested that an early form of the coronavirus had infected mice. In their scenario, it evolved into Omicron in rodents and then infected humans again.

Anyway, Omicron became dominant within weeks that followed its discovery due to its mutations. . Some of them allowed the virus to slip inside cells more successfully. Others let it escape some of the antibodies from vaccines or previous infections.

Most antibodies stick to "spike" proteins on the surface of coronaviruses, preventing them to enter our cells. But some of Omicron's mutations changed parts of the spike protein so that some of the stronger antibodies couldn't stick to it anymore.

So as Omicron multiplied, it continued to mutate. New versions emerged, but for the first few months they replaced each other like a series of waves crashing on a beach. The first version, BA.1, was superseded by BA.2, then BA.5, both of which evaded some antibodies produced in earlier Omicron infections.

But in February, Theodora Hatziioannou, a virologist at Rockefeller University in New York, and her colleagues conducted an experiment that suggested Omicron was poised for an evolutionary explosion.

Dr. Hatziioannou's team tested Omicron against 40 different antibodies that could still block the variant. They found that it was remarkably easy for a few more mutations to make it resistant to almost all of these antibodies.

Amazingly, when the researchers added these same mutations to the spike protein from the original version of the coronavirus, there was no effect on its antibody resistance. Dr. Hatziioannou suspected that Omicron's large number of new mutations were altering its evolutionary landscape, making it much easier to evolve even more resistance.

"We were actually worried when we saw that,” she said.

Over the months that followed, Omicron lived up to those concerns. Thanks to the large number of Omicron infections, the virus had more opportunities to mutate. And...