Omicron variant: simple cold or Covid-19?

On November 26, 2021, WHO designated variant B.1.1.529 as a variant of concern, named Omicron, on the advice of the WHO Technical Advisory Group on Virus Evolution (TAG-VE). This decision was based on evidence presented to the TAG-VE that Omicron has several mutations that may impact its behavior, such as the ease with which it spreads or the severity of the disease it causes. Here is a summary of what is currently known.