Why Omicron is the most worrying Covid variant yet

The discovery of a new and potentially vaccine-resistant Covid variant has concerned governments and unnerved markets around the world. Omicron has prompted the return of border closures and mandatory testing and mask wearing as countries attempt to slow its number of mutations on its spike protein - the part of the virus vaccines use to prime the immune system - has concerned scientists, but it will take weeks to determine the extent of the threat Omicron poses. The Guardian’s science correspondent Linda Geddes explains Subscribe to Guardian News on YouTube ► Omicron: everything you need to know about new Covid variant ►