The deadliest pandemic in history: the 1918 influenza outbreak

12-0137-009 influenza

Thousands died in 2009 with the outbreak of swine flu that swept the globe. However that figure pales in comparison to the estimated 50 to 100 million deaths that resulted from the 1918-1919 influenza pandemic that followed World War One.

The disease was unusual from an epidemiological standpoint as it attacked in 3 separate waves across a 12 month period. While influenza usually peaks in winter, the first wave began in the spring of 1918. It spread rapidly across the globe and closely resembled seasonal flu. A second wave from September to November was highly deadly and the final wave in early 1919 was less virulent than either of the previous two outbreaks.

An exceptionally severe virus, it was contracted by about 500 million people. This means one third of the global population at the time was affected. The loss of life was unprecedented; the fatality rate was over 2.5% compared to the rate of 0.01% of seasonal outbreaks. The illness came on suddenly and quickly progressed to respiratory failure. In cases that developed more slowly people often died from secondary bacterial infections.

The 1918 flu also targeted sufferers differently to milder strains. Normally the people worst affected by influenza are either the very young, the elderly or the immunocompromised. In the 1918 pandemic healthy young adults aged 20-35 were the hardest hit. In America, the death rate for 15-34 year olds was 20 times higher in 1918 than in previous years.

Although the origin of the virus is unknown, it spread worldwide along trade routes and shipping lines. Even remote Pacific islands and parts of the Arctic were affected.  The mass movement of people associated with the war and demobilisation of troops afterwards is thought to have helped spread the illness. Quarantines were introduced to reduce the spread of the disease, however they were of limited effectiveness.

Medical services were stretched to their limits and public health measures attempted to control the outbreak. Public gatherings were suspended and many shops stayed closed during the worst periods of the pandemic. People took to wearing gauze masks and stayed indoors until as quickly as it had appeared, the pandemic ended.

While the exact strain that caused the 1918 pandemic hasn’t been identified, it is thought to have evolved from an avian virus. Genomic sequencing of the entire virus is yet to be completed, however it is known that the H1N1 strains circulating today are descended from the influenza of the 1918 pandemic.

If you’d like to follow up on this short post, you can take a look at an infographic on the 1918 flu here. To compare, there is one on the 2009 swine flu here.

Image credit

Navy Medicine. (1918). Influenza [Image]. Retrieved from


Taubenberger, J. K. & Morens, D. M. (2006). 1918 influenza: the mother of all pandemics. Emerging Infectious Diseases, 12(1), 69-79.