>> reporter: just 24 hours after that green light for a second booster for people over 50, president biden rolling up his sleeve. >> we have the pfizer, we have thmoderna. >> reporter: across the country today, many americans doing the same after the cdc said another round of boosters were especially important for those people over 65 and those over 50 with underlying conditions. >> i think that's a really good idea, because especially with people stopping wearing masks now, there's going to be another surge, definitely and >> reporter: and tonight, the world health organization, tracking those surging, warning it's seeing "intense circulation" of the omicron subvariant ba.2, which is also now dominant in the u.s. the highest concentrations in new york, new jersey, and new england, where it makes up mre than 70% of new cases. >> what we're concerned about here in the u.s. is a potential surge of the new ba.2 variant. and we have to think about all the tools that we have at our disposal. >> reporter: today, the cdc