It means Covid-19 transmission is now high, or rising at an ever-increasing rate.
4 UK CMOs – inc @DrGregorSmith – agree raising of #Covid_19 alert level to 4. I’ll participate in COBR meeting tomorrow am, after which @scotgov Cabinet will agree measures to bring virus back under control in Scotland. I’ll then offer statement to @ScotParl tomorrow pm.
— Nicola Sturgeon (@NicolaSturgeon) September 21, 2020