Scientists rapidly identified the Omicron variant. But firm answers about its impact could take weeks

The emergence of the Omicron variant of the coronavirus, with a suite of mutations that suggests it might be extra transmissible and be able to evade at least some immune protection, has the world eager for answers about what it means for the Covid-19 pandemic. But so much remains unknown largely because the variant appears to have been detected and publicized so quickly.

With other variants, a matter of months passed between the time they were first documented until they were designated “variants of concern” — in some cases giving scientists...