West Nile virus: What the US Data Actually Shows

The published figures

Every number below is reproduced from a primary source and carries that source beside it. Where a figure is absent it is shown as unavailable rather than estimated — the reasoning for each gap is set out further down this page.

Figures are West Nile virus–specific (ArboNET). WNV caused 1,808 reported US human cases in 2024 (92% of all notifiable arboviral disease) with 173 deaths; 91% of reported cases were neuroinvasive (the severe form). Case-fatality and hospitalization rates here are therefore among REPORTED cases, which skew severe — an estimated 80% of WNV infections are asymptomatic and never counted. Reported WNV cases swing widely year to year with mosquito activity.

What this data cannot tell you

1 of the five funnel metrics has no publishable US figure for West Nile virus. That is a deliberate result, not an oversight. Where no primary source publishes a comparable figure, this site leaves the cell empty rather than filling it with an estimate, a number borrowed from a different population, or a single-study result presented as a general rate.

• Severe Outcome Rate — no comparable figure published by the record's primary source as of 2026-07-24.

This matters when comparing viruses. A blank cell is not a low number: it means the measurement does not exist, and treating it as zero would make West Nile virus look safer than the evidence supports. The comparison table on the Virus Risk Perspective page applies the same rule — unavailable figures are excluded from ranking rather than sorted to the bottom.

How West Nile virus compares

Ranked only against viruses in this collection that publish the same metric. Viruses without a published figure are excluded from each comparison rather than counted as zero, so the denominator differs from metric to metric.

Read the case comparison carefully. Records in this collection do not all measure exposure the same way. Some report confirmed cases counted by a surveillance system (measles, West Nile), others a modelled estimate of total annual illness including cases that are never reported (norovirus, seasonal influenza). A modelled burden figure will always dwarf a confirmed-case count, so a gap on this metric can reflect how a disease is counted as much as how often it occurs. The per-figure sources above state which basis each number uses.

How the figures have moved

Each observation below is a figure as it stood on a given date, with the source that published it. Points are not interpolated: where an agency published a figure once, one point is shown rather than a line drawn through invented values.

Global picture

WHO reports that about 80% of West Nile infections are asymptomatic and roughly 1 in 150 (~0.67%) develop severe neuroinvasive disease. No global annual case or death count is published. Fact sheet re-read 2026-09-15: it is dated 3 October 2017 — older than the 2024-12-31 previously recorded here, so the date is corrected backwards to the sheet's own date. WHO has published no newer West Nile fact sheet; the ~1-in-150 severe-disease proportion is a standing figure CDC also states.

Source: WHO — West Nile virus fact sheet · Data as of 2017-10-03 · Surveillance confidence: moderate

Sources

• CDC MMWR — West Nile Virus and Other Nationally Notifiable Arboviral Diseases, United States, 2024 primary source · retrieved 2026-07-24
• WHO — West Nile virus fact sheet primary source · retrieved 2017-10-03
• CDC — Historic Data, West Nile Virus (ArboNET) primary source · retrieved 2016-12-31

Sourcing tiers, and the rule that a derived figure inherits its weakest input's tier, are set out on the Our Sources page. The process behind every figure is described in How We Answer Questions.