June 1918

Spanish flu

The lethal second wave of the 1918 influenza pandemic emerges at Atlantic ports

The lethal wave seemed to ignite at widely separated Atlantic ports within days of each other: Brest, Freetown and Boston.

Mid-to-late August 1918: three ports, one turn

During mid-to-late August 1918, unusually lethal influenza outbreaks emerged at or near Atlantic ports — Brest in France, Freetown in Sierra Leone, and Boston in the United States. A severe Boston outbreak was recognised on 27 August, associated with a troopship arriving from Brest, and spread rapidly into the northeastern United States and its military installations.

Wartime ships, railways, troop concentrations and crowded camps carried the infection efficiently between ports, camps and continents.

Not the pandemic's beginning

These outbreaks marked the emergence of the deadly second wave, not the moment influenza first became pandemic: a generally milder first wave had already moved through parts of North America, Europe and possibly Asia from March through the summer.

The frightening change was a sharp transition from that milder wave to outbreaks associated with far greater pneumonia mortality. The catastrophic worldwide mortality peak followed in the autumn.

What remains unknown

The virological reason the second wave was more severe remains unresolved. So does the toll: a modern demographic reassessment estimates about 15 million deaths in 1918 plus 2.5 million in 1919, while the CDC retains the widely quoted figure of at least 50 million for the whole pandemic. No source consulted supports the old claim that more than 30 million died in the six months after August 1918.

The name is misleading too — 'Spanish flu' reflects Spain's relatively open wartime reporting, not the outbreak's origin.

Sources

Researched 23 Aug 2026 6 sources 3 audit passes Date disputed

How this was checked

Researched from the web into a fact sheet, rewritten from that sheet, then audited against it by a different model. How the pipeline works →

Date disputed. Sources disagree; the research places it at ~1918-08.

What the sources leave uncertain

The listing is internally inconsistent: its slug and supplied date say June 1918, while its title says August.
There was no single day on which the disease “became pandemic.” The milder first wave had already spread through parts of North America, Europe and possibly Asia from March through the summer.
Scholars identify several near-simultaneous late-August outbreaks, so August 1918 is best treated as an approximate period marking the lethal second wave’s emergence.
Global mortality estimates vary greatly because registration was incomplete and scholars use different definitions and extrapolation methods. A modern demographic reassessment estimated about 17.5 million deaths across 1918–19, while the CDC retains the widely quoted figure of at least 50 million.