library. >> reporter: the world health organization and cdc declared omicron a variant of concern after it was flagged by scientists in south africa. a mutation in the omicron variant causes a peculiar test result called an s-gene drop out. >> the green curve is the s-gene. it would normally be up there with them. >> reporter: making a suspicious case easy to spot for expedited sequencing. >> we have about six samples right now that have that signature s-gene drop out. >> reporter: but sequencing is required to confirm omicron because it isn't the only variant with that type of marker. scientists say they've seen many throughout the pandemic. some like delta become the dominant strain while others fade quickly. right now there is no way to know what type of impact omicron could have on the u.s. but they agree when it comes to cracking covid knowledge is