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2009Peer-reviewed · 2 sourcesWell documented

A Decade-Old Pig Virus Becomes the First 21st-Century Flu Pandemic

An H1N1 strain that had circulated unnoticed in central Mexican pigs for years suddenly gains the ability to spread between people

On the timeline · around 2009 · Emerging ThreatsEmerging ThreatsA Decade-Old Pig Virus Becomes the First 21st-Century Flu Pandemic1990199520002005201020152020

Quick facts

Pathogen
Novel H1N1 influenza strain, swine-origin
First identified
La Gloria, Veracruz, Mexico
WHO alert raised
Phase 6 (highest level), June 11, 2009
Incubation in pigs
About a decade before human transmission began, per genomic research
Significance
First influenza pandemic of the 21st century

What happened

In 2009 a new influenza strain, a reassortment of bird, swine, and human flu genes combined with a Eurasian pig flu virus, began spreading among people after first being identified in La Gloria, a rural town in Veracruz, Mexico. On June 11, 2009 the World Health Organization raised its pandemic alert to Phase 6, its highest level, indicating sustained community transmission on at least two continents, making this the first influenza pandemic of the 21st century. Genomic research published years later established that the parent virus had circulated undetected in pig populations in a small region of central Mexico for roughly a decade before a version emerged capable of jumping into humans, and that the original swine strains were still present in those pig populations at the time of the research.

Why it matters

The 2009 pandemic showed that a pandemic-capable flu strain can incubate for years in an animal reservoir, invisible to human surveillance, before crossing over, a pattern distinct from 1918's more sudden emergence and a reminder that influenza surveillance in livestock, not just in hospitals, matters for catching the next pandemic strain early.

How we know

Retrospective genomic sequencing of the virus and of related strains still circulating in Mexican pigs, published in eLife, traced the reassortment history and the roughly decade-long incubation period in swine before human transmission began.

Sources

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A Decade-Old Pig Virus Becomes the First 21st-Century Flu Pandemic · Pandemics Through History · SourcedStory