What we know — and don’t know — about the omicron variant

As cases of infection with the omicron variant of the coronavirus multiply around the world, scientists are racing to characterize the heavily mutated variant to understand how it spreads and gauge new risks during this wave of the pandemic.

Preliminary studies released this month have offered some clues about the effectiveness of vaccines against the omicron variant and whether it causes more severe illness, but much remains uncertain, and more research is needed.