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In the year In November 2021, almost two years after the coronavirus emerged in Wuhan and spread around the world, the surprises seemed to be over. More than four billion people have been infected with the virus and five million people have died. Two new variants, known as Alpha and Delta, rose and then fell. As Thanksgiving approaches, many Americans plan to head out for the holiday.

And then the next day in Turkey, the outbreak offered a big new surprise. Researchers in Botswana and South Africa have warned the world that a highly modified virus has emerged and is spreading rapidly. As the World Health Organization called the variant, Omicron quickly surpassed other strains of the virus. It continues to dominate now, in its second year.

In the two years since its discovery, the omicron has become not only incredibly contagious, but also an evolutionary marvel that challenges many of the pre-pandemic assumptions of virologists. It has spawned many species that are adept at finding new victims by evading immunity.

“It was like another outbreak,” said Adam Lauring, a virologist at the University of Michigan.

Dr. Lauring and other Omicron watchers are trying to make sense of the past two years to prepare for the future. Omicron can become a permanent part of life, changing like seasonal influenza. But researchers warn that the virus still has the potential to surprise us, especially if we stop paying attention.

When Omicron first came to light, the United States and other countries mistakenly believed that they would halt its distribution by banning travel from South Africa. In fact, it is already widely distributed. Within a few days, Britain, Italy and Germany had found OMRON with positive covid tests.

Omicron’s gift for rapid propagation is the result of several mutations. By changing the shape of the virus, antibodies produced by vaccines or previous infections are unable to attach to it and prevent the virus from entering cells.

“It was the first virus to fundamentally investigate how to evade the immune system,” said Dr. Jacob Lemieux, an infectious disease specialist at Massachusetts General Hospital.

Dr. Lemieux and several other Omicron experts suspect they have discovered a new mutation that is infecting a person’s weakened immune system. Immunocompromised people are able to fight off some of the coronaviruses in the body during the virus, allowing the rest to acquire mutations that interfere with the immune system.

“It will be like a laboratory for virus evolution,” said Peter Markov, a virologist at the London School of Hygiene and Tropical Medicine.

Epidemiologists As they watched the Omicron wave in late 2021, they saw a significant difference from previous surgeries. Compared to previous variants, Omicron kept a smaller fraction of infected people hospitalized. One reason for this change is that many people have become immune to earlier strains of the coronavirus. Our immune system includes not only antibodies, but also specialized immune cells that recognize and kill infected cells. This is the second line of defense They are even connected to Omicron.It prevents many new infections from becoming serious.

Still, Omicron caused many new infections – the first wave killed about half of all Americans A recent estimate – still caused a terrible wave of hospitalizations.

In the year In early 2022, the Omicron wave hit the United States and most other countries. China managed to tame the storm with its “zero Covid” policy, but protests against its draconian nature grew so strong that President Xi Jinping abruptly dropped it in November 2022. The floodgates opened: in just a few weeks, more than a billion Chinese people took Omicron, and as a result More than a million deaths.

As the omicron moved from person to person, the offspring acquired many mutations. Sometimes, two micron viruses would slide in the same cell, which would produce new hybrid viruses by combining their genes. One of these so-called recombinations combines two sets of escape mutations and hits a peak. The result was a new hybrid called XBB.

XBBs easily infect humans, even those already infected with Alpha, Delta, or early Omicrons. As a result, in early 2023, XBB became dominant in the United States.

Vaccine makers have tried to keep up with Omicron’s rapid evolution. In August 2022, the Food and Drug Administration approved booster vaccines targeting the BA.5 Omicron variant, which was then dominant. In September 2023, the agency approved the XBB shot. But XBB is fading now, because more escape variables have evolved.

“We’re in chaos right now,” says Mark Johnson, a virologist at the University of Missouri.

Several Omicron experts say the chaos may end soon. In August, a variant called BA.2.86 emerged with a new mutation — the result of possibly re-evolution in an immunocompromised human.

Initially, BA.2.86 did not appear to be based on genetic potential due to its inability to expand rapidly. “If genetics were the only thing that mattered, it would get its own Greek letter,” says Thomas Peacock, a virologist at the Pirbright Institute in Woking, England. “But BA.2.86 was a bit of a wet squib.”

However, in the past few months, the BA.2.86 lineage seems to have kicked into high gear, acquiring a mutation that allows it to remove more antibodies. JN.1, as this mutated form is known, has become a highly resistant version of the coronavirus. It seems to be growing fast in France, and may soon expand to other countries.

It is difficult to predict the future path of a new variant like JN.1. Its success depends on what kind of defenses it encounters when it spreads from host to host. At the beginning of the epidemic, things were simple because no one was immune to the corona virus.

“In the beginning we were one big nursery,” says Michael Lassig, an evolutionary biologist at the University of Cologne.

Today, by contrast, most people on Earth are immune to one form or another from natural infection, vaccination, or both. Dr. Lassig said, “The virus affects a very complex ecosystem.”

This global immunity means that fewer people die than when the epidemic began. Still, Omicron’s damage is still severe. US Centers for Disease Control and Prevention found Between October 2022 and September 2023, more than 80,000 people died from Covid-19, eight times more than the number of deaths from influenza.

As Omicron continues to evolve, epidemiologists still see benefits for vaccines. Justin Lessler, a researcher at the University of North Carolina, and his colleagues recently made a prediction about Covid infections. He came to the conclusion It has been reported that annual vaccination campaigns can save up to 49,000 lives a year.

Those vaccines will be more effective if they are updated to keep up with the evolving virus. But Katrina Lithgow, a biologist at the University of Oxford, worries that progress will slow when governments stop paying for genetic sequencing of new variants.

“If we don’t put things in order, we won’t see them,” she said.

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