Powassan 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.

case_fatality_rate_pct (13.2%) and hospitalization_rate_pct (92.2%) are §12a derivations from CDC's own ArboNET totals for all reported US Powassan disease cases 2004–2025 (63 deaths and 439 hospitalizations among 476 cases; data current as of June 2, 2026), superseding the 11% CDC 2006–2016 cohort figure and the 91.7% Tier 2 systematic-review figure, both retained as earlier history points. annual_deaths_estimate is the 2024 final count (9). severe_outcome_rate_pct left UNAVAILABLE: Powassan neuroinvasive disease is the only form nationally notifiable, so any 'severe outcome' percentage drawn from this surveillance stream would reflect ascertainment bias (mild/non-neuroinvasive infections are essentially never captured) rather than a true population rate.

How these figures were calculated

2 figures above are arithmetic rather than a number lifted straight from an agency page. Both inputs are given below with their own source, geography, and reporting period, so the calculation can be checked rather than taken on trust. A derived figure is never rated more reliable than its weakest input.

What this data cannot tell you

1 of the five funnel metrics has no publishable US figure for Powassan 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 2026-06-02.

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 Powassan 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 Powassan 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.

Sources

• CDC — Historic Data (2004-2025), Powassan Virus, ArboNET (data current as of June 2, 2026) primary source · retrieved 2026-06-02
• Kakoullis L, Vaz VR, Kaur D, et al. — Powassan Virus Infections: A Systematic Review of Published Cases, Trop Med Infect Dis. 2023;8(12):508 peer-reviewed estimate · retrieved 2023-11-26

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.