H5N1 Avian Influenza

STAGE: FORMING

FAO/WHO/WOAH, 18 May 2026 (data as of 1 March 2026): global public health risk assessed as "low" and "unchanged from the previous risk assessment," with risk for occupationally or frequently exposed persons "low to moderate." CDC situation summary (last updated 6 March 2026): "the current public health risk is low."

The symptoms

	symptom	the evidence	as of
✅	Human case count and trend (official tallies)present	WHO cumulative table records 997 confirmed human A(H5N1) cases from 25 countries since 2003, 478 fatal (CFR 47.9%). CDC counts 1,022 cases worldwide since 1997. Cases remain sporadic and animal-exposure-linked: 12 new infections outside the US from Aug 2025 to Jun 2026 (Bangladesh, Cambodia, India), 3 fatal; the US has 71 cases and 2 deaths since Feb 2024. Trend is low and episodic, not accelerating in humans. [source]	2026-06-26
✅	Documented mammal-to-mammal transmission chainspresent	Peer-reviewed work documents mammal-to-mammal spread: an H5N1 outbreak in elephant seals in Argentina (Nat Commun 2024) and cross-species plus mammal-to-mammal clade 2.3.4.4b transmission with PB2 adaptations in Chile (Nat Commun 2025). US dairy cattle sustain cow-to-cow spread. First US H5N1 detection in northern elephant seals occurred in California in Feb 2026. CDC states mammal-to-mammal spread is 'thought to be rare, but possible.' These chains are in animals, not humans. [source]	2026-05-18
✅	US dairy-cattle epizootic — current statepresent	Since 2024 and as of 1 Mar 2026, 1,088 dairy herds across 19 US states have tested positive for A(H5N1) (FAO/WHO/WOAH). California released all dairies from H5N1 quarantine on 27 Feb 2026 but remains at Stage 3 (continued testing and monitoring). Nine bovine outbreaks were reported to WOAH between 1 Jul 2025 and 1 Mar 2026. The National Milk Testing Strategy continues nationwide. Emory sampling on 14 California farms (PLOS Biology) found infectious virus in milking-parlor air and wastewater — an unproven-in-humans but flagged alternative exposure route. [source]	2026-03-01
—	Human-to-human transmission (the decisive symptom)absent	FAO/WHO/WOAH, 18 May 2026: 'To date, no human-to-human transmission has been identified through epidemiologic, virologic and serologic investigations, although investigations for some cases are ongoing.' The viruses 'remain avian-adapted, without established mammalian adaptive mutations or the capacity for sustained human-to-human transmission' and 'would require additional genetic changes to acquire efficient human-to-human transmission via respiratory droplets.' A CDC ferret study of a D1.1 virus (A/Washington/239/2024) showed no respiratory-droplet transmission. This is the symptom that would move the stage; it is not present. [source]	2026-05-18
◐	Vaccine and antiviral readinesspartial	WHO GISRS maintains candidate vaccine viruses matched to circulating clade 2.3.4.4b; the most recent CVV update was published Feb 2026. Some manufacturers have initiated production of an A(H5) human vaccine matching current strains; updated WHO guidance on licensed A(H5) vaccines was published Dec 2025. Circulating viruses remain susceptible to neuraminidase-inhibitor antivirals; oseltamivir is more than 90% of the US stockpile but is roughly 4-fold less potent against 2.3.4.4b than 2.3.2.1c, and some sequence markers of reduced lab susceptibility to oseltamivir/baloxavir have appeared — clinical significance uncertain. Readiness exists but is not a licensed, distributed population vaccine. [source]	2026-05-18
◐	Surveillance gapspartial	FAO/WHO/WOAH repeatedly recommends increased surveillance, including in areas 'where surveillance in animals may be limited,' and notes minimal human seroprevalence data. Retrospective serology has revealed previously undetected farmworker infections, indicating undercounting. OFFLU's 2026 report 'Beyond poultry' flags under-monitoring of mammal spillover. Gaps are acknowledged by the institutions themselves, not resolved. [source]	2026-05-18

The honest read

Base rate first: H5N1 has infected humans since 1997, roughly 1,000 cumulative cases across about 29 years, and despite decades of sporadic spillover plus the ongoing dairy-cattle and poultry epizootics, it has never achieved sustained human-to-human transmission. What almost always happens is what is happening now — isolated, animal-exposure-linked cases that dead-end without onward human spread. The high historical case-fatality rate (WHO CFR near 48%) reflects severe but rare zoonotic infections, not pandemic spread, and is likely inflated by undercounting of mild cases. The single indicator that would change this stage is documented human-to-human transmission chains, or an official upgrade of the risk word above "low" for the general population; the animal-side indicators are moving, but the human-risk language is explicitly unchanged.

The watch

A future automated watcher polls: WHO "Risk assessments and summaries of influenza at the human-animal interface" (https://www.who.int/teams/global-influenza-programme/avian-influenza/monthly-risk-assessment-summary) — updated approximately monthly, with periodic joint FAO/WHO/WOAH assessments. Cross-check against CDC "A(H5) Bird Flu: Current Situation" (https://www.cdc.gov/bird-flu/situation-summary/index.html), updated as events warrant.. Until then, the stage is reviewed by hand against the same sources — and says so.