Omicron splinters into fast-spreading lineages, highlighting coronavirus’s evolution

A burgeoning form of Omicron, called BA.2.12.1 — itself a sublineage of the BA.2 branch — now accounts for nearly one in five cases of Covid-19 in the U.S.

Scientists around the world are discovering and tracking newer forms of the Omicron coronavirus variant, showing how even when a strain becomes globally dominant, it continues to evolve and can splinter into different lineages.

Case in point: Updated data released Tuesday showed that a burgeoning form of Omicron, called BA.2.12.1 —  itself a sublineage of the BA.2 branch of Omicron — now accounts for nearly one in five infections in the United States. It’s eating into the prevalence of the ancestral BA.2, highlighting the emergent virus’s transmission advantage over its parent. BA.2 now accounts for about 74% of cases, while the remaining 6% or so are from the BA.1 branch of Omicron, the first form of the variant that took over globally and whose prevalence has been falling as BA.2 became dominant.

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