In spring 2020, shortly after the pandemic began, many scientists predicted that the coronavirus would not evolve particularly fast.

But those predictions have been upended time and again — and never more so than with omicron, a variant with an astonishing number of mutations that is rampaging through Europe and South Africa. In New York, cases are suddenly soaring to record levels as holiday parties and sports games are canceled, and California officials are bracing for a similar crisis in the coming weeks.

Once again, uncertainty and worry are rising. No one knows what the next Greek letter variants will unleash.