H5N1 Bird Flu vs Seasonal Flu: Two Fatality Rates for One Virus
Seasonal influenza makes about 51 million Americans ill a year and kills around 0.09% of them. H5N1 has infected 70 people in the United States since 2024 and killed one — a 1.43% rate — while WHO's worldwide table gives 40% for 2025. All three numbers are correct. This page puts the two influenzas on the same funnel and explains why H5N1 has two fatality rates, and why neither is the risk to a person.
How to read this page. The tables are the network's two data records side by side — nothing is re-typed, so a figure here is exactly the figure on each virus's own page, with the same source, tier and date. A fatality rate is only comparable when its denominator is the same, and it usually is not; each cell carries its denominator note, and the prose below says which comparisons hold and which do not. An empty cell is a stated absence of measurement, not a low number.
The Figures, Side by Side
Avian influenza A(H5N1)
A type of bird flu (influenza A H5N1) that mainly infects birds and some mammals; human cases are rare and usually linked to close contact with infected animals, but can be severe.
Emerging in the US An emerging US situation: human cases are rare and tied to close contact with infected animals, with no sustained person-to-person spread.
Evolving situation: CDC's current situation summary (March 6, 2026) still describes an ongoing situation: A(H5) is widespread in wild birds and causing outbreaks in poultry and US dairy cows, with sporadic human cases in farm workers; CDC rates the current public health risk as low and reports no person-to-person spread. On July 7, 2025 CDC folded bird-flu updates into its routine influenza reporting. The last US H5N1 human case had onset in February 2025; the one later US A(H5) case (November 2025) was the world's first human A(H5N5) infection and was fatal. Global historical H5N1 mortality is around 50%, but US cases have been overwhelmingly mild by comparison.
Seasonal influenza
The seasonal flu, a contagious respiratory illness caused by influenza viruses that circulate each winter; it ranges from mild to severe and is preventable by annual vaccination.
Common in the US Circulates every US winter, causing tens of millions of illnesses and tens of thousands of deaths a year.
United States, side by side
| Metric | Avian influenza A(H5N1) | Seasonal influenza |
|---|---|---|
| Annual Exposure / Cases | 70 CDC — A(H5) Bird Flu: Current Situation (updated March 6, 2026) primary source as of 2026-03-06 | 51,000,000 CDC — 2024-2025 Influenza Season Summary: Severity, Disease Burden, and Burden Prevented primary source as of 2026-03-12 |
| Severe Outcome Rate | Data not available | Data not available |
| Hospitalization Rate | Data not available | Data not available |
| Case Fatality Rate | 1.43% CDC — A(H5N1) Bird Flu Response Update, March 19, 2025 (deaths ÷ cases, both cumulative US outbreak totals) primary source as of 2025-03-19 Of reported US H5N1 cases in the 2024–25 outbreak; most were mild farm-worker infections. Re-verified 2026-09-15 against CDC's current situation summary (March 6, 2026): no further H5N1 cases or deaths since the March 2025 inputs. CDC's page now counts all A(H5) subtypes — 71 cases and 2 deaths — because the 71st case (Washington, November 2025, fatal) was an A(H5N5) infection (WHO DON 590), which sits outside this H5N1 record. | 0.09% CDC — 2024-2025 Influenza Season Summary (deaths ÷ illnesses, both same-season US modeled estimates) primary source as of 2026-03-12 Of symptomatic illnesses (CDC modeled burden). |
| Annual Deaths | 1 CDC — A(H5) Bird Flu: Current Situation (updated March 6, 2026) primary source as of 2026-03-06 | 45,000 CDC — 2024-2025 Influenza Season Summary: Severity, Disease Burden, and Burden Prevented primary source as of 2026-03-12 |
| Reported cases per 100,000 residents | 0.02 CDC cumulative US H5N1 outbreak case count ÷ US Census 2024 population estimateofficial statisticsas of 2024-07-01 | Data not available |
Avian influenza A(H5N1) — record note: 70 is a cumulative outbreak total (April 2024 onward) rather than a clean annual figure. CDC's situation summary (updated March 6, 2026) reports 71 A(H5) cases and 2 deaths since February 2024 across all H5 subtypes; one of those — the November 2025 Washington case — was confirmed as A(H5N5), not H5N1 (WHO DON 590, 5 December 2025), so the H5N1 figures are 71 − 1 = 70 cases and 2 − 1 = 1 death. WHO's cumulative H5N1 table (data as of 7 August 2026) agrees: United States 67 cases / 1 death with 2024 onset, 3 / 0 in 2025, 0 in 2026. CDC's exposure breakdown of the 71: 41 dairy herds, 24 poultry farms and culling operations, 3 other animal exposure, 3 unknown. No human-to-human transmission identified. cases_per_100k and case_fatality_rate_pct are derivations per SITE-PLAYBOOK.md §12a from the March 19, 2025 CDC update — the counts have not changed since, so the inputs stand — both explicitly labelled as covering the outbreak-to-date window (not a calendar year) and, for CFR, the mild US outbreak specifically (not the far higher global historical H5N1 rate).
Seasonal influenza — record note: 2024-25 was classified 'high severity' — the most severe season since 2017-18. CDC's own long-run range (2010-2025) is 9.4M-51M illnesses and 6,300-52,000 deaths, so this single season sits at the top of that range. case_fatality_rate_pct is a same-record derivation (deaths ÷ illnesses, both CDC 2024-25-season modeled estimates) per SITE-PLAYBOOK.md §12a; both inputs are model-based CDC burden estimates, not raw notified counts, since seasonal influenza isn't individually reportable. The illnesses and deaths trends use CDC's modeled disease-burden estimates (same method each season), one point per season from 2017-18 through 2024-25 — deaths: 52,000 (2017-18), 28,000 (2018-19), 22,000 (2019-20), 6,300 (2021-22), 21,000 (2022-23), 28,000 (2023-24), 45,000 (2024-25). The 2020-21 season is intentionally absent: CDC published no burden estimate for it because influenza circulation was minimal under COVID-19 mitigation. These modeled burden figures are NOT the smaller coded death-certificate counts, which are a different series and are not mixed in.
Global, side by side
| Metric | Avian influenza A(H5N1) | Seasonal influenza |
|---|---|---|
| Annual Exposure / Cases | 30 WHO — Cumulative number of confirmed human cases for avian influenza A(H5N1) reported to WHO, 2003–2026 (data as of 7 August 2026) primary source as of 2026-08-07 | 1,000,000,000 WHO — Influenza (seasonal) fact sheet primary source as of 2025-02-28 |
| Severe Outcome Rate | Data not available | Data not available |
| Hospitalization Rate | Data not available | Data not available |
| Case Fatality Rate | 40% WHO — Cumulative number of confirmed human cases for avian influenza A(H5N1) reported to WHO, 2003–2026 (data as of 7 August 2026) (deaths ÷ cases, calendar year 2025) primary source as of 2025-12-31 Of WHO-confirmed cases worldwide in 2025. WHO reports only laboratory-confirmed cases, which skew heavily toward severe illness in countries where mild infections are rarely tested, so this is a reported-case fatality proportion, not an infection fatality rate. The cumulative 2003–2026 figure is 479 ÷ 1,002 = 47.8%; the mild US outbreak (1.43%) sits at the other extreme. | Data not available |
| Annual Deaths | 12 WHO — Cumulative number of confirmed human cases for avian influenza A(H5N1) reported to WHO, 2003–2026 (data as of 7 August 2026) primary source as of 2026-08-07 | 290,000–650,000 WHO — Influenza (seasonal) fact sheet primary source as of 2025-02-28 |
Avian influenza A(H5N1) — global note: WHO's cumulative table of confirmed human A(H5N1) cases (data in WHO HQ as of 7 August 2026) gives 30 cases and 12 deaths with onset in calendar year 2025 — the latest complete year — and 1,002 cases / 479 deaths in total since 2003 (for the United States it counts cases reported as A(H5) too). 2026 to 7 August: 9 cases, 2 deaths (partial year, not charted). Annual counts by onset year, 2020–2025: 1, 2, 6, 12, 81, 30 cases and 0, 1, 1, 4, 4, 12 deaths. CDC's own tally (June 26, 2026) is 1,022 cases worldwide since 1997. The WHO Influenza (avian and other zoonotic) fact sheet, re-dated 21 January 2026 and re-read 2026-09-15, still gives no precise total ("hundreds of human cases, and many deaths"), so the table is cited instead. Surveillance confidence is low: only laboratory-confirmed cases are counted and testing of mild illness varies widely by country.
Seasonal influenza — global note: WHO estimates ~1 billion seasonal influenza cases worldwide each year, including 3–5 million cases of severe illness and 290,000–650,000 respiratory deaths. Fact sheet re-read 2026-09-15: dated 28 February 2025 (the date now carried here) and unchanged — the ~1 billion cases and 290,000–650,000 deaths are WHO's standing estimates, restated rather than re-derived.
Sources behind every figure above
- CDC — A(H5) Bird Flu: Current Situation (updated March 6, 2026) primary source as of 2026-03-06
- CDC — A(H5N1) Bird Flu Response Update, March 19, 2025 (deaths ÷ cases, both cumulative US outbreak totals) primary source as of 2025-03-19
- WHO — Cumulative number of confirmed human cases for avian influenza A(H5N1) reported to WHO, 2003–2026 (data as of 7 August 2026) primary source as of 2026-08-07
- CDC — 2024-2025 Influenza Season Summary: Severity, Disease Burden, and Burden Prevented primary source as of 2026-03-12
- WHO — Influenza (seasonal) fact sheet primary source as of 2025-02-28
What the Comparison Shows
Scale first. The US table is a study in orders of magnitude: 51,000,000 seasonal influenza illnesses against 70 H5N1 infections; 45,000 deaths against 1; a fatality rate of 0.09% against 1.43%. H5N1's reported-case rate of 0.02 per 100,000 residents is a derivation the record shows in full — an outbreak-to-date count over the Census population, labelled as covering April 2024 onward rather than a calendar year. Seasonal flu's equivalent cell is unavailable because CDC publishes a modelled illness burden, not a reported-case count, and the two should not be set against each other as though they were the same kind of number.
The two H5N1 fatality rates are both real, and they measure different populations. The US 1.43% is one death among 70 detected infections in an outbreak in which, as the record's note says, "most were mild farm-worker infections" found by actively testing exposed workers. WHO's global 40% for 2025 (12 deaths among 30 confirmed cases) and its 479 deaths among 1,002 cases since 2003 count laboratory-confirmed cases in countries where, the record notes, "testing of mild illness varies widely" — so the confirmed cases are disproportionately the severe ones. Same virus family, different clades and exposures, and above all a different denominator: the US figure includes the mild cases that active surveillance found; the global figure largely does not. Neither is the probability that an infected person dies, which nobody can compute without knowing how many mild infections were never tested.
What makes seasonal flu the bigger killer and H5N1 the bigger worry. Seasonal influenza's toll comes from volume: a sub-0.1% rate applied to a fifth of the population every winter. H5N1's concern is the opposite shape — almost no human cases, "no human-to-human transmission identified" (record note), a CDC public-health risk assessment of "low", and a historical global mortality "around 50%" that would matter enormously if the transmission side ever changed. The evolving-situation note on the card is the live status: widespread in wild birds, outbreaks in poultry and dairy cattle, sporadic farm-worker cases, updates folded into routine influenza reporting since July 2025, and one later fatal A(H5N5) case that sits outside this H5N1 record.
Globally. WHO estimates about a billion seasonal influenza cases and 290,000–650,000 respiratory deaths a year; H5N1's annual counts by onset year for 2020–2025 are 1, 2, 6, 12, 81 and 30 cases. The 81 is 2024, the year the US dairy outbreak was found — and the reason it is 81 rather than a handful is that the United States tested people who were not very ill.
Frequently Asked Questions
Is H5N1 deadlier than seasonal flu?
Per confirmed case worldwide, far deadlier — 40% in 2025 and 479 deaths among 1,002 cases since 2003 (WHO). Per detected US infection in the 2024–25 outbreak, 1.43% (1 of 70). The gap is the denominator: the US count includes mild infections found by testing exposed workers; the global count is mostly people ill enough to be tested. Seasonal flu's 0.09% is of all symptomatic illnesses.
Which kills more people?
Seasonal influenza, by four orders of magnitude: about 45,000 US deaths a year and 290,000–650,000 worldwide, against one US H5N1 death since 2024 and 12 worldwide in 2025.
Is H5N1 spreading between people?
No — the record's note, from CDC's situation summary, is "no human-to-human transmission identified", and CDC rates the public-health risk as low. Human cases are tied to contact with infected animals.
Why does the 2024 global count jump to 81?
Because the United States found and tested mild infections in dairy and poultry workers. Most other years' counts are dominated by severe cases in countries with less testing of mild illness — which is also why the global fatality rate is so high.
This comparison is statistical and epidemiological. It is not medical advice or a risk assessment for any individual; the network's spoke pages cover symptoms, treatment and what to do about exposure for each virus.