Omicron rapidly dominating in South Africa; US reports first case

Heavily mutated Omicron is rapidly becoming the dominant variant of the coronavirus in South Africa less than four weeks after it was first detected there, and the United States on Wednesday became the latest country to identify an Omicron case within its borders.

The first known US case was a fully vaccinated person in California who returned to the United States from South Africa on Nov 22 and tested positive seven days later.

The person had...