Omicron, the newest coronavirus variant, is also the quickest to be labeled a "variant of concern" by the World Health Organization because of its seemingly fast spread in South Africa and its many troubling mutations.
Its emergence has already led to travel restrictions, high-level government meetings and promises by vaccine makers to start working on strain-specific vaccines just in case.
But it has a long way to go to take over from Delta, the variant that dominates all over the world. And the long list of variants that at first frightened the world before falling off the map can be a reminder that viruses are unpredictable.
Here's a look at the named coronavirus variants. WHO designates coronavirus variants as either variants of concern -- meaning they look dangerous enough to bear close scrutiny and continual updates -- or as variants of interest, or variants under monitoring. Only five currently meet the definition for variants of concern: Alpha, Beta, Gamma, Delta and Omicron.