New COVID variant NB.1.8.1, or Nimbus, is spreading rapidly in the US, accounting for over one-third of cases.

While COVID-19 transmission remains low in the US, health experts are anxious about the potential for a big summer wave as ...

NB.1.8.1 — a new COVID-19 variant tied to a surge in China — now accounts for around 37% of cases in the U.S., according to variant proportion estimates from the CDC. Four notes: ...