By November 2021, nearly two years after the coronavirus emerged in Wuhan, China, and spread across 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, known as alpha and delta, had surged and then ebbed. As Thanksgiving approached, many Americans were planning to resume traveling for the holiday.
And then, the day after the turkey, the pandemic delivered a big new surprise. Researchers in Botswana and South Africa alerted the world that a highly mutated version of the virus had emerged and was spreading fast. Omicron, as the World Health Organization called the variant, swiftly overtook other forms of the virus. It remains dominant now, on its second anniversary.
In the two years since its emergence, omicron has proved to be not only staggeringly infectious but also an evolutionary marvel, challenging many assumptions virologists had before the pandemic. It has given rise to an impressive number of descendants, which have become far more adept at evading immunity and finding new victims.
"It was almost like there was another pandemic," said Adam Lauring, a virus expert at the University of Michigan.
Lauring and other omicron watchers are trying to make sense of the past two years in order to prepare for the future. It's possible that omicron will become a permanent part of life, steadily mutating like seasonal influenza. But researchers warn that the virus still has the capacity to surprise us, especially if we stop paying close attention.
When omicron first came to light, the United States and other countries wrongly believed they could stop its spread by banning travel from South Africa. In reality, it had already spread far and wide. In a matter of days, Britain, Italy and Germany discovered omicron in positive COVID tests.
Omicron's gift for spreading fast was the result of dozens of mutations. They altered the virus' surface, so that antibodies produced by vaccines or previous infections could not stick tightly to it and prevent the virus from invading cells.
"It was the first virus to figure out in a major way how to escape immunity," said Dr. Jacob Lemieux, an infectious disease specialist at Massachusetts General Hospital.