president's address and afterwards as well. thank. what a difference a day makes. yesterday as we went to air, you'll recall the latest cdc breakdown showed the delta variant accounted for the vast majority of cases other in the u.s. today the cdc's updated numbers show a complete flip. omicron is now making up almost three out of four new infections nationwide. the entire trajectory of the pandemic changing overnight for americans. let's bring in cnn medical correspondent ecohen. elizabeth, experts knew omicron would eventually be dominant. did they know would happen so fast? break it down for us. >> reporter: i'm not sure that they knew that it would happen quite this fast. this has really been incredible. we remember when the so-called uk variant, that's what it was called at the time, when that took over. that was fast. when delta took over, that was fast t.wasn't as fast as this. let take a look at what happened -- has happened just in the past two weeks.