By November 2021, almost two years after the coronavirus emerged in Wuhan, China and spread throughout the world, the surprises seemed to be over. More than 4 billion people had been vaccinated against the virus and 5 million had died. Two new variants, Alpha and Delta, had emerged and then declined.
And then researchers in Botswana and South Africa alerted the world that a highly mutated version had emerged and was spreading rapidly. Omicron, as the World Health Organization called the variant, quickly overtook other forms. He is still dominant.
Omicron has proven to be an evolutionary marvel. It has given rise to an impressive number of offspring, who have become much more adept at evading immunity.
“It was almost like there was another pandemic,” said Adam Lauring, a virologist at the University of Michigan.
Omicron’s gift for rapid propagation was the result of dozens of mutations. They altered the surface of the virus so that the antibodies could not adhere firmly to it and prevent the virus from invading the cells.
“It was the first virus to significantly figure out how to escape immunity,” said Jacob Lemieux, an infectious disease specialist at Massachusetts General Hospital.
He and other experts suspect that the variant acquired its new mutations while infecting a single person with a weak immune system. Immunocompromised people can only fight off some of the coronaviruses in their bodies, allowing those that remain to acquire mutations.
As epidemiologists followed the Omicron wave in late 2021, they saw a crucial difference from previous waves. Omicron sent fewer infected people to the hospital. One reason was that many people had immunity to earlier forms. Our immune defenses include not only antibodies, but also immune cells that can recognize and kill infected cells. This second line of defense resisted the Omicron, preventing many of the new infections from becoming serious.
Still, Omicron caused so many infections that it unleashed a devastating wave of hospitalizations.
As Omicron passed from person to person, his descendants acquired more mutations. Sometimes two Omicron viruses ended up in the same cell, producing new hybrid viruses with a mixture of their genes. One of these recombinations mixed two sets of evasive mutations. The result was a new hybrid called XBB.
XBB easily infected people, even those who had already been infected with Alpha, Delta, or earlier forms of Omicron.
Vaccine makers tried to keep up. But XBB is now declining as even more evasive variants have evolved.
“Right now we are in a period of chaos,” said Marc Johnson, a virologist at the University of Missouri.
Several experts said the chaos could end soon. A variant called BA.2.86 emerged in August.
At first, BA.2.86 failed to spread quickly. However, in recent months, the BA.2.86 lineage appears to have accelerated, gaining a mutation that allows it to evade even more antibodies. JN.1, as this mutated form is known, has become the most resistant version of the coronavirus. It appears to be growing rapidly in France and may spread soon.
The success of JN.1 will depend on the type of immune defenses it encounters. Today, most people have immunity in one form or another, whether from infection, vaccination, or both. This means that fewer people will die than at the beginning of the pandemic.
By: CARL ZIMMER
BBC-NEWS-SRC: http://www.nytsyn.com/subscribed/stories/7003104, IMPORTING DATE: 2023-11-27 20:10:07
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