With BA.2.12.1 now dominant in US, experts eye new subvariants BA.4 and BA.5 [Updated]

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Update 6/7/2022 2:00 pm ET: The Centers for Disease Control and Prevention updated its prevalence estimates for coronavirus variants Tuesday and has now provided separate estimates for omicron subvariants BA.4 and BA.5, which were previously reported together. Based on data collected up to June 4, BA.5 is estimated to account for 7.6 percent of US cases, while BA.4 is estimated to account for 5.4 percent. BA.2.12.1 is still the dominant variant in the US, estimated to account for 62.2 percent of cases.

Original story 6/6/2022 6:17 pm ET: Omicron subvariant BA.2.12.1 has overtaken BA.2 as the dominant version of the pandemic coronavirus in the US, now accounting for an estimated 59 percent of cases nationwide. But BA.2.12.1's reign may end as quickly as it began, with yet another batch of omicron subvariants gaining ground—BA.4 and BA.5—and threatening to cause more breakthrough infections.

BA.2.12.1 has a transmission advantage over BA.2, which itself has an edge over the initial omicron subvariant, BA.1, that caused a towering surge of US cases in mid-January. BA.2 peaked in mid-April, accounting for 76 percent of US cases at its height. But then came BA.2.12.1, which is named for being the 12th lineage stemming from BA.2 and the first branch of that BA.2.12 lineage.