Omicron’s sister variant spreads faster. So why did the one we call Omicron hit first?

Two years into a pandemic that turned us all into amateur virologists, we’ve learned that the best-spreading coronavirus variant will outcompete any slowpokes. But something curious happened with Omicron: The more transmissible version didn’t take off first. The virus that the world came to know as Omicron — and that ignited outbreaks in countries around the world — is just one lineage that made up the broader Omicron grouping. It’s known officially as BA.1. For some time, its sister viruses, including one named BA.2, didn’t seem to be doing much.