COVID-19 Summer Surge Spreads to All 43 States as Nimbus Variant Dominates

A summer COVID-19 surge is now spreading across all four U.S. census regions, driven by the highly transmissible Nimbus variant (NB.1.8.1). The CDC confirms COVID is growing or likely growing in 43 states as of mid-August 2026. Emergency department visits attributed to COVID peaked at 1.7% nationally last summer, double the 1% winter peak. The virus remains relatively mild for most people, but experts warn older adults, infants, and immunocompromised individuals face serious risk.

Nimbus variant now accounts for 43% of sequenced cases

The Nimbus variant (NB.1.8.1), a descendant of the JN.1 Omicron lineage, accounted for approximately 43% of all sequenced U.S. COVID cases as of late June 2026, according to CDC genomic surveillance data. The variant first drove surges in China, Singapore, and Southeast Asia in early 2026 before being detected in the United States through international airport screening in March. In Singapore, the variant spread at roughly 60% weekly growth rates before reaching dominance, a trajectory that public health officials cited as a leading indicator of its likely U.S. spread.

Summer has become the peak season, not winter

COVID-19 is shifting from a winter disease to a summer phenomenon in the United States. COVID-related emergency department visits peaked last summer in late August at 1.7% of all visits, compared to just 1% during the winter peak. In California, the pattern is even more pronounced: summer 2025 peaked at 2.1% of emergency visits, while winter 2025 reached only 0.2%. Dr. Erica Pan, director of the California Department of Public Health, stated in a recent briefing that the ’25-’26 vaccines remain effective and highly recommended given the current surge.

Spread is nationwide but still relatively mild

The virus is now spreading across all four U.S. census regions, though the South and West remain the hardest hit. Dr. John Brooks, an infectious disease doctor at Emory University and former CDC official, stated that the virus is ticking up pretty much everywhere nationally. California is one of only four states where COVID wastewater activity levels are considered moderate or high. Despite the spread, hospitalizations and deaths remain low compared to 2021, when weekly COVID deaths spiked above 15,000 nationally around Labor Day and peaked at more than 21,000 in late January.

Herd immunity and vaccination offer protection

The milder severity of this summer’s wave reflects growing herd immunity and vaccination coverage. Dr. Brooks noted that more people have had one or more infections plus multiple vaccinations, offering substantial protection. However, COVID still causes serious disease for vulnerable populations. The disease can force healthy people to miss work and school for a week or two, and it remains dangerous for older adults, infants, and immunocompromised individuals, sometimes requiring hospitalization or causing death.

Final Thoughts

The 2026 summer COVID surge marks a structural shift in the virus’s seasonality, now peaking in summer rather than winter. With Nimbus accounting for 43% of sequenced cases and spreading across 43 states, travelers and workers should consider updated vaccines and remain cautious around vulnerable populations.

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