THE RECORD
What changed
H1N1 influenza infected the world, killed tens of millions and caused unusually high young-adult mortality.
EVIDENCE
What remains
Death records, newspapers, hospitals and viral genomes from preserved tissue establish scale and agent.
WHY IT MATTERS
Why it matters
It highlighted public health, nursing, statistics and distancing measures.
OPEN QUESTION
Where interpretation begins
Spanish flu does not identify origin; the name reflects freer Spanish reporting, while origins remain uncertain.