The CDC's Friday situation report holds the cumulative dairy-cattle count at 18 states and 70 confirmed human H5N1 cases since the dairy outbreak began in March 2024. [1] Idaho remains on the active vector watch — the last state added to the affected list in April — with no new herd detections this week and no genotype change reported in the National Veterinary Services Laboratories sequencing queue. [3] The headline number is the absence of a number.

Yesterday's edition described the testing infrastructure that produces this stillness. USDA's APHIS loosened its interstate movement testing requirement for lactating dairy cattle six weeks ago, citing supply-chain pressure from producers. Pre-movement testing now applies only to cattle leaving herds with active detections — not the universal lactating-cow PCR USDA had imposed in April 2024. The loosening was paired with an expanded bulk-tank surveillance regime that covers fewer cows but more dairies. The two regimes do not produce equivalent data.

The Wisconsin D1.1 detection in December was the last reminder that the system can shift. D1.1 is the genotype that crossed from wild birds to dairy cattle on a single Nevada farm in January 2025 — a host jump that surveillance had not flagged until the cows were already symptomatic. APHIS told CIDRAP last week that bulk-tank surveillance would catch a D1.1-class shift inside two weeks. The April 2024 system would have caught it inside three days. [2]

The 70-case human number stays flat. The 18-state animal number stays flat. The vector-watch architecture is what holds them flat, and it is now thinner than it was last spring.

-- KENJI NAKAMURA, Tokyo