Omicron’s radical evolution

Omicron’s radical evolution

Subject – Science and Tech

Context – record-breaking wave of omicron cases

Concept –

• When the omicron variant took off in southern Africa in November, scientists were taken aback by its genetic makeup. Whereas earlier variants had differed from the original Wuhan version of the coronavirus by a dozen or two mutations, omicron had 53 — a shockingly large jump in viral evolution.
• An international team of scientists found that 13 of those mutations were rarely, if ever, found in other coronaviruses, suggesting they should have been harmful to omicron. Instead, when acting in concert, these mutations appear to be key to some of omicron’s most essential functions.
  • Some mutations were shared by omicron, delta and other variants, suggesting that they had arisen several times and that natural selection had favored them over and over again.
  • What makes these 13 mutations all the more intriguing is that they’re not randomly sprinkled across omicron’s spike. They form three clusters, each altering a small portion of the protein. And each of those three areas play a big part of what makes omicron unique.
  • Two of the clusters change the spike near its tip, making it harder for human antibodies to stick to the virus and keep it out of cells. As a result, omicron is good at infecting even people who have antibodies from vaccinations or a previous COVID infection.
  • The third cluster of mutations alters the spike closer to its base. This region, known as the fusion domain, swings into action once the tip of the spike has hooked onto a cell, enabling the virus to deliver its genes inside its new host.
  • Typically, coronaviruses use the fusion domain to merge with a cell’s membrane. Their genes can then float away into the depths of the cell.
  • But omicron’s fusion domain usually does something different. Rather than merging into the cell membrane, the whole virus gets swallowed up in a kind of cellular sink hole, which pinches off to form a bubble inside the cell. Once the virus is captured inside the bubble, it can break open and release its genes.
  • This new pathway to infection may help to explain why omicron is less severe than delta. The cells in the upper airway can readily swallow up omicron in bubbles. But deep in the lungs, where COVID can cause life-threatening damage, coronaviruses have to fuse to cells, which omicron doesn’t do well.

Mutations in coronavirus

• Mutations are a regular part of a coronavirus’s existence. Every time a virus replicates inside of a cell, there’s a small chance that the cell will create a flawed copy of its genes. Many of those mutations would make new viruses defective and unable to compete with other viruses.
• But a mutation can also improve a virus. It could make the virus stick more tightly to cells, for example, or make it replicate faster. Viruses that inherit a beneficial mutation may outcompete others.
• Over most of 2020, scientists found that different lineages of the coronavirus around the world gradually picked up a handful of mutations. The evolutionary process was slow and steady, until the end of the year.
• In December 2020, British researchers were jolted to discover a new variant in England carrying 23 mutations not found in the original coronavirus isolated in Wuhan, China, a year before.
  • That variant, later named alpha, soon swept to dominance worldwide. Over the course of 2021, other fast-spreading variants emerged.
• While some remained limited to certain countries or continents, the delta variant, with 20 distinctive mutations, ousted alpha and became dominant over the summer.
• And then came omicron, with more than twice as many mutations.