health expert has warned that omicron is probably the most significant threat to public health since the pandemic began. and covid is now more likely than a cold in london. new rules come into effect this week, including covid passes being necessary to enter certain venues. also in terms of how people should act if they do come in contact with a covid case. previously, the guidance had been you should self-isolate. now, the guidance from the government, you should do daily covid tests instead. already, this is causing huge disruption, the number of cases as people race to get their boosters. the strategy right now, get boosters into people s arms as quickly as possible. a pandemic truism is what happens in europe comes to the united states soon enough. cnbc s julianna tatelbaum, stay safe. still ahead, white house press secretary karine jean-pierre, she joined me ahead of the president s trip to tornado-ravaged kentucky.