Influenza pandemic
epidemic of an influenza virus that spreads on a worldwide scale and infects a large proportion of the human population
An influenza pandemic is an epidemic of an influenza virus that spreads across a large region (either multiple continents or worldwide) and infects a large proportion of the human population. There have been five major influenza pandemics in the last 140 years, with the 1918 flu pandemic being the most severe; this is estimated to have been responsible for the deaths of 50–100 million people. The 2009 swine flu pandemic resulted in under 300,000 deaths and is considered relatively mild. These pandemics occur irregularly.
Influenza pandemics occur when a new strain of the influenza virus is transmitted to humans from another animal species. Species that are thought to be important in the emergence of new human strains are pigs, chickens and ducks. These novel strains are unaffected by any immunity people may have to older strains of human influenza and can therefore spread extremely rapidly and infect very large numbers of people. Influenza A viruses can occasionally be transmitted from wild birds to other species, causing outbreaks in domestic poultry, and may give rise to human influenza pandemics. The propagation of influenza viruses throughout the world is thought to be in part by bird migrations, though commercial shipments of live bird products might also be implicated, as well as human travel patterns.
The World Health Organization (WHO) has produced a six-stage classification that describes the process by which a novel influenza virus moves from the first few infections in humans through to a pandemic.
This brief starts where responsible research should: with the source description of “Influenza pandemic” as epidemic of an influenza virus that spreads on a worldwide scale and infects a large proportion of the human population. Everything that follows is an evidence route, not borrowed authority.
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The subject matters to the general reference register because the source frames it as epidemic of an influenza virus that spreads on a worldwide scale and infects a large proportion of the human population. Its deeper value depends on whether names, dates, institutions and citations support that framing.
Named sources, stable identifiers and responsible institutions provide the strongest route from overview to verifiable evidence. The source revision retrieved here is dated Sep 6, 2026. The linked authority identifier is Q2723958. None of the 0 selected statements returned an explicit reference. The first chronological checks are 1918 and 2009.
Overview language is designed for orientation and should not be treated as a substitute for the evidence cited beneath it. The source lead contains qualifying language; that uncertainty should survive quotation, summary and reuse. Authority statements aid reconciliation but still require their own references, qualifiers and ranks to be checked.
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This entry incorporates text from “Influenza pandemic” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.