Question: How quickly is the BA.2 variant spreading in the US?

Answer: The CDC tracks variants across the country (see Q&A of 1/13/22).  According to CDC’s most recent update of 2/16, the highly contagious BA.2 variant (currently considered a variant of omicron) is increasing in prevalence across the country, representing ~4% of all cases the week of 2/12 (95% Prediction Interval* 2.8% – 5.3%).  This reflects a doubling from the previous week, which was double the week before that (Figure).  The BA.2 variant is estimated to be 30% more contagious than the original omicron variant. As you can see in the Figure, BA.2 is more prevalent on the East Coast and West Coast.  Of note, the delta variant has disappeared from circulation across the country. We’ll know in the coming days whether BA.2 continues its exponential growth trajectory.  The bad news is that BA.2 is even more contagious and existing antibody treatments may be less effective.  The good news is that it does not appear to cause more serious illness than omicron BA.1.  Many scientists think that BA.2 will prolong the omicron wave, though some are concerned that it could cause a new wave if it takes a bigger foothold.  

*Note: Prediction Interval (PI) is similar to Confidence Interval (CI), but it has more uncertainty than CI, and therefore a wider range of values than the CI.  

Figure. 3.9% of all variants the week of 2/12 were BA.2, up from 1.6% the week before (from CDC)