Previous Pandemics

How often do influenza pandemics occur?

Influenza pandemics have occurred every few decades. There were three influenza pandemics in the last century.

What happened in the previous pandemics?

Previous pandemics affected large numbers of the population, caused many deaths, and resulted in severe economic and social disruption.

Spanish Flu

Year: 1918-1919
Estimated deaths: 20-40 million (global)
Age groups most affected: Healthy young adults (20-50 years)
Likely origin: Uncertain

Asian Flu

Year: 1957-1958
Estimated deaths: 1 million (global)
Age groups most affected: Very young and very old
Likely origin: China

Hong Kong Flu

Year: 1968-1969
Estimated deaths: 1-4 million (global)
Age groups most affected: Very old and those with underlying medical conditions
Likely origin: China

When is the next pandemic due?

No one knows for sure. Intervals between previous pandemics have varied with no recognizable pattern. Also, a pandemic may not follow the usual seasonal pattern of ordinary influenza and could occur at any time of the year.