New CDC transmission estimates released Friday, Aug. 1 show the effective reproduction number, or Rt, above one in 40 states, meaning overall US infections are again expanding.
In 28 states the agency assigns its highest confidence category -- "growing" -- while another 12 fall into the "likely growing" bucket. No state is currently classified as declining, and nine are holding steady.
For more info, view the CDC's interactive map here, and click on a specific state.
Nationally, the Rt sits at one point one one, with a greater than 99.99 chance that infections are increasing.
Emergency-department data reinforce the trend: COVID-19 visits have ticked upward for three consecutive weeks.
The virus' resurgence is being driven by yet another version of Omicron. Genomic surveillance for the two weeks ending July 27 finds variant NB 1.8.1 responsible for 43 percent of sequenced US cases, displacing older cousins such as KP 2 and JN 1.
Public-health researchers say NB 1.8.1 carries spike-protein changes that appear to improve immune evasion, though clinical severity has not changed markedly.
Rt is considered a leading indicator, often turning upward weeks before hospitalizations rise.
CDC epidemiologists caution that sustained transmission could strain clinics as schools reopen in August and seasonal viruses return in the fall.
Officials urge high-risk Americans to stay current with vaccinations, test when symptomatic, and improve indoor ventilation -- a trio of steps that still blunt spread even as the virus evolves.
Nationwide, a reformulated monovalent vaccine targeting the latest Omicron lineages is expected to debut next month, but its arrival may trail the current surge unless infections ebb on their own.
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