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| Why Omicron is still the main variant of the new coronavirus |
Haven't arrived at "Pi" (Pi) yet?
Last year, the World Health Organization began using Greek letters to name new and feared new variants of the coronavirus. They started with the Greek letter Alpha and changed rapidly over the ensuing months. In less than a year, "Omicron" (Omicron), which was launched in November, is already the 13th mutant strain to be named.
But it's been 10 months since Omicron's first appearance, and the next Alphabet has yet to be launched.
This does not mean that SARS-CoV-2, the coronavirus that causes COVID-19, has stopped evolving. But it may have entered a new phase. Over the past year, more than a dozen common viruses have independently transformed into new major public health threats. But now, all the most important variants of the virus come from the same lineage: the Omicron.
David Robertson, a virologist at the University of Glasgow, said: "Based on what has been detected so far, it appears that future SARS-CoV-2s will evolve from Omicron."
Moreover, it appears that Omicron also has a remarkable ability to continue to evolve. The latest subtype variant, BA.2.75.2, is better at evading immune responses than all previous americon variants.
BA.2.75.2 is still extremely rare, accounting for only 0.05% of the new coronaviruses sequenced globally in the past three months . But so did the other Aomecron subtypes that went on to dominate the world . If BA.2.75.2 spreads this winter, it could make Moderna and Pfizer's newly authorized booster shots less effective.
Mutations can occur each time SARS-CoV-2 replicates within cells. In rare cases, mutations may help SARS-CoV-2 replicate faster. Or it may help the virus evade antibodies produced after previous infection with the new coronavirus.
This mutation, which favors the virus's survival, may become more common in a country before dying out. Or it could spread to the whole world.
The evolution of SARS-CoV-2 started out as a slow and steady process, as scientists expected based on other coronaviruses. Its evolutionary tree gradually splits into branches, each acquiring some mutations. Evolutionary biologists track them by meaningful but arcane code names. No one but them pays attention to these code names because they don't affect how sick the virus makes people.
But a later lineage defied expectations, and it was originally called B.1.1.7 . When British scientists discovered it in December 2020, they were surprised to find that it carried a unique sequence containing 23 mutations. These mutations allow it to spread faster than other versions of the virus.
Within months, several other worrisome variants emerged around the world—each with its own combination of mutations, and each with the potential to spread rapidly and cause a spike in deaths. For ease of communication, WHO has chosen the Greek alphabet system. B.1.1.7 became alpha.
Different variants have experienced varying degrees of success. Alpha started to dominate the world, while " Beta " only spread in South Africa and a few other countries before dying out.
Even more puzzling, these variants arose independently. Beta doesn't come from alpha. Instead, it arose from a new set of mutations from a different branch of the SARS-CoV-2 evolutionary tree. This is true of all Greek-named variants down to Omicron.
It is likely that most of these variants acquired the mutation through hiding. Instead of spilling over from one host to another, they cause chronic infections in people with weakened immune systems.
Unable to mount a powerful attack, the viruses hide in patients for months, accumulating mutations. When viruses finally emerge from their hosts, they already possess an astonishing array of new capabilities—finding new ways to invade cells, weaken the immune system, and evade antibodies.
"It emerged like an invasive species," says computational biologist Ben Möller of the Karolinska Institutet in Stockholm.
Omicron was extraordinarily lucky in this genetic lottery, picking up more than 50 new mutations that helped it find new ways to enter cells and infect people who were vaccinated or previously infected. Most of the other variants died out as it spread around the world and caused an unprecedented surge in cases.
"The genetic innovation seen in Omicron is much more profound, as if it were a new species rather than just a new strain," says Darren Martin, a virologist at the University of Cape Town.
But it soon became apparent that the name "Omicron" hid a complicated reality. After the original Omicron virus evolved in the fall of 2021, its descendants split into at least five clades, known as BA.1 to BA.5.
Over the next few months, the subtypes took turns becoming dominant. BA.1 took the lead, but was quickly defeated by BA.2. Each is unique enough to evade some of the immunity of the previous. By this summer, BA.5 was on the rise.
In response, the FDA invited vaccine makers to produce a booster shot that included the BA.5 protein and a protein from the original version of the virus. Currently, 85% of new crown cases in the United States are caused by BA.5, and these booster shots are being promoted to the public.
But scientists say BA.5 will likely fade away before winter. The Omicron is always evolving - possibly sometimes jumping between hosts, sometimes hiding in one of them for months.
Since these new lineages belonged to Omecron, they did not have their own Greek alphabet. But that doesn't mean they're just slightly modified versions of the original. Antibodies that work against earlier forms of Omicron do not perform well against newer forms of Omicron.
"They could actually be given different Greek letters," Robertson said.
BA.2.75.2, identified just last month , is one of the newest grandchildren of Omicron. According to Morrell, it's also the most elusive Omicron to date. In laboratory experiments, he and colleagues tested BA.2.75.2 against 13 monoclonal antibodies in clinical use or development. It escaped all antibodies except Bebtelovimab, made by Eli Lilly.
They also tested for antibodies from recent Swedish blood donors. BA.2.75.2 is significantly superior to other Omecron subtypes in evading these defenses.
The researchers posted their study online Friday . Researchers at Peking University came to similar conclusions in a study released the same day . Neither study has yet to be published in a scientific journal.
Morell cautioned that scientists have yet to conduct experiments to demonstrate the effectiveness of BA.5 enhancements against BA.2.75.2. He suspects that getting a lot of BA.5 antibodies offers some protection, especially against severe disease.
"It's still important, but we'll have to wait for the data to know exactly how effective this antibody is," Morell said.
There is no reason to expect BA.2.75.2 to be the end of the evolutionary line. As immunity to previous versions of Omecron grows, the new version will also evolve viruses capable of evading immunity.
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