South Africa, where Omicron was first identified, has the world's highest rate of HIV, which weakens the immune system and increases a person's vulnerability to infections with common-cold viruses and other pathogens. In that part of the world, there are many people in whom the recombination that added this ubiquitous set of genes to Omicron might have occurred, Soundararajan said.
"We probably missed many generations of recombinations" that occurred over time and that led to the emergence of Omicron, Soundararajan added.
More research is needed to confirm the origins of Omicron's mutations and their effects on function and transmissibility. There are competing hypotheses that the latest variant might have spent some time evolving in an animal host.