How it unfolded
- SpringFirst wave: many people get sick, but few die. Many countries barely notice it amid the war.
- FallThe second wave is the deadliest. Most of the deaths occur during this wave.
- WinterThe third wave is weaker. The number of people who have already had the illness grows, making it harder for the virus to find new people to infect.
- After thatThe outbreaks fade. Descendants of the virus continue circulating among people for decades.
The second wave is the biggest mystery of that epidemic. The fall wave killed a disproportionate number of young and healthy people, which is unusual for the flu; explanations are still being debated, and there is no single answer.
A significant share of the deaths was caused not by the virus itself, but by bacterial pneumonia that followed. Antibiotics did not yet exist, and this largely determined the mortality rate.
Why cities were affected differently
Comparing American cities became a textbook example. Where mass gatherings were canceled in the first few days, the death curve was noticeably lower; where a parade went ahead despite warnings, it was several times higher.
Speed and duration were what mattered. Restrictions introduced early and lifted gradually produced the best results; those introduced late helped little, while those lifted too soon led to a new rise.
The measures were the same ones we know today: closing schools and theaters, banning gatherings, isolating people who were sick, and requiring masks. Nothing fundamentally new has appeared in this area since then.
The virus itself, however, did not disappear. Its direct descendants caused seasonal flu for decades, and its genome was sequenced from tissue samples preserved in permafrost.
What stopped the 1918 pandemic?
What did mortality in different cities depend on?
Sources
- The 1918-1920 flu pandemic ended without specific treatment or vaccines
- a significant share of deaths was linked to secondary bacterial pneumonia. Comparing cities showed that mortality depended on the timing and duration of non-pharmaceutical restrictions
Next in the “Epidemics” series
2 articles in full on the site, 3 more in the app
