A COVID subvariant that drove surges in China, Singapore, and parts of Southeast Asia has now become the dominant strain circulating in the United States — and while overall national activity remains moderate, wastewater surveillance shows rising viral levels in 10 states, concentrated in the South and West.
The variant, known as NB.1.8.1 and informally called "Nimbus," is a descendant of the JN.1 Omicron lineage. By the two-week period ending late June 2026, it accounted for an estimated 43% of COVID cases in the United States, according to CDC genomic surveillance data. NB.1.8.1 surpassed all other circulating variants in that period to become the dominant U.S. strain.
