We have the first study (still un-peer-reviewed) that advances an evidence-based hypothesis for why Omicron COVID may actually produce milder disease. I want to emphasize this is a single study, which has not undergone peer review. The gist is that Omicron was much faster at taking hold in the air passage leading to the lungs but much less efficient in replicating in lung tissue. The surmise is that this makes it much better at jumping from host to host – which is demonstrated by rate of spread in multiple countries – but much less efficient at creating illness once it gets into the lungs.