New omicron offshoot ticks up in US: 4 notes

The highly transmissible omicron subvariant BA.5 remains dominant in the U.S. But another omicron offshoot, BA.4.6, is slowly gaining traction, CDC estimates on variant proportions show. 

Four things to know:  

1. BA.4.6 accounted for 6.3 percent of COVID-19 cases in the week ending Aug. 20, up from 5.6 percent of cases a week earlier, CDC estimates show. The latest data suggests it has outpaced BA.4, which is now estimated to account for 4.3 percent of cases. 

2. Scientists are still trying to learn more about BA.4.6, which is currently most prevalent in Midwestern states — Iowa, Kansas, Missouri and Nebraska. Across those states, it accounts for nearly 16 percent of cases, estimates show. 

3. BA.4.6 has a mutation that allows it to evade immunity, much like other omicon subvariants. "It has a specific mutation in the spike protein, and some of the BA.5 lineages have also had that, so it's hard to know if having had BA.5 will protect us from BA.4.6," Sharon Welbel, MD, director of hospital epidemiology and infection control for Chicago-based Cook County Health, told NBC Chicago. A study published Aug. 10 in the preprint server bioRxiv suggests BA.5 infection would likely not protect against reinfection from BA.4.6.

4. Over the last three months, BA.4.6 has had a growth advantage of 41 percent over BA.5 in the U.S., Raj Rajnarayanan, PhD, said in an Aug. 16 tweet, citing data from a global COVID-19 variant dashboard that he runs. Dr. Rajnarayanan is the assistant dean of research and associate professor in the department of basic sciences at the New York Institute of Technology College of Osteopathic Medicine at Arkansas State University in Jonesboro.


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