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After a slow start, the Omicron BA.2 subvariant is making serious inroads here in the United States, with its share of cases doubling to 23.1%, up from last week's 11.6% estimate. As the above map illustrates, BA.2 rates appear to be highest in New England, and on the east and west coasts, and lower in the Midwest and south.
For now, BA.1.1 remains dominant at 66% nationally, but at the rate BA.2 is gaining, dominance will likely shift to BA.2 over the next couple of weeks. B.1.1.529 - which was the dominant Omicron variant in December - has now been whittled down to just over a 10% share.
While data on the impact of BA.2 is still limited, in European countries where it has become dominant, we haven't seen any compelling evidence suggesting it is any more severe than BA.1.1. But it does transmit more efficiently, and that likely is contributing to the recent upticks in infections we've seen in Europe (see Where COVID is Rising).
BA.2 is also reportedly driving the Hong Kong and Chinese outbreaks of COVID.
In Hong Kong, case fatality rates - particularly among the (mostly unvaccinated) elderly - have climbed dramatically, suggesting that Omicron's `mild reputation' may be due in large part to its spread in highly vaccinated European populations.
The latest CDC Nowcast estimate follows:
