Still at low levels in the US, but should eventually become dominant in the coming months.
It appears to have a growth advantage over BA.1. This might be due to increased transmissibility or a shorter serial interval or both. No notable differences in vaccine effectiveness against it. Too early to tell if BA.2 has different severity than BA.1.
Also too early to know if BA.1 infection provides cross-immunity to BA.2 reinfection (generally reinfections occur 90+ days after the initial infection, so it is too early to see BA.1 reinfections). But for unvaccinated people with prior infections to pre-Omicron variants, reinfection risk against BA.2 is high.