A new COVID-19 subvariant called NB.1.8.1 — nicknamed "Nimbus" — has become the dominant strain circulating in the United States, accounting for an estimated 43% of sequenced COVID cases as of late June 2026, according to CDC genomic surveillance data. As the variant's prevalence climbs and wastewater surveillance detects rising viral levels in 10 states, health officials are urging high-risk individuals to confirm their vaccine status before the summer season reaches its peak.
National COVID activity remains low overall, according to the CDC's July 6 respiratory illness summary. However, the pattern of a new dominant variant emerging alongside rising wastewater signals in multiple states is consistent with the early stages of the summer COVID waves that have occurred every year since 2020.
