Case counts for the US appear to have peaked at a 7-day average of 806k on Jan 14. Omicron grew from approximately 35k daily cases on Dec 14 to ~800k daily cases in ~4 weeks. 1/9 
Looking at cases per 100k population per day across states, downturns are clear in NY, NJ, MA, FL, etc..., but many states are not yet at peak case loads. 2/9
If we partition @CDCgov cases between Delta and Omicron using @GISAID sequence data following approach by @marlinfiggins (bedford.io/papers/figgins…) we can see clear Omicron epidemics. 3/9
These epidemics have proceeded in a similar fashion across states with initial rapid exponential growth that slowed as epidemics grew in size. It appears that states are largely on the same curve, just some are farther ahead on this curve compared to others. 4/9
We estimate that as of Jan 17 the US as whole has had a cumulative ~15M confirmed cases of Omicron, or approximately 4.5% of the population recorded as confirmed cases. The large majority (>90%) of these accumulated since Dec 14. 5/9
Assuming between a 1 in 4 and 1 in 5 case reporting rate suggests that between 18% and 23% of the country was infected by Omicron by Jan 17, with the large majority infected in a span of just ~4 weeks. 6/9
https://twitter.com/trvrb/status/1480610447522816005
There may be a longer tail of circulation after the peak (as seen in South Africa), but a rough expectation would have an equivalent number of cases in the next 4 weeks on the other side of the peak. This would suggest 36-46% of the US infected by Omicron by mid-Feb. 7/9
Having ~40% of the population infected by a single pathogen in the span of 8 weeks is remarkable and I can't think of an obvious modern precedent. Flu seasons generally have perhaps 10% infected in the span of 16 weeks. 8/9
My big question now is to what extent will Omicron-like emergence events characterize "endemic" circulation of SARS-CoV-2? Given it occurred once, having it occur again would not be at all surprising, but I don't know whether to expect this every year or every ten. 9/9
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