“In principle, mutations can also work against each other,” said Jesse Bloom, an evolutionary biologist at the Fred Hutchinson Cancer Research Center in Seattle. “However, in this case evolutionary selection is more likely to lead to the spread of a new variant with favorable than unfavorable combinations of mutations.”

Still, this phenomenon, called epistasis, is why scientists are reluctant to speculate on Omicron’s attributes, even though individual mutations in the variant are associated with greater transmissibility or with an ability to dodge the body’s immune defenses…

Omicron has a cluster of mutations that are all linked to tighter binding to human cells. “But acting together, they might have a somewhat different effect,” Dr. Bloom said. For that reason, he added, he cannot predict how the variant will act in the body.