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A new international study published in the International Journal of Epidemiology, co-led by RMIT researcher Dr Lauren Steele and LCDS researcher Dr Andrea Tilstra, examines how mortality risks varied by age across four major influenza pandemics (1918, 1957, 1968, and 2009), drawing on mortality data from 48 populations.
The findings revisit a long-standing narrative shaped by the 1918 influenza pandemic, which saw unusually high mortality among young adults. While this pattern has often informed expectations about pandemic risk, the new analysis shows that later pandemics were strikingly different from 1918. In 1957, 1968, and 2009, age-specific mortality patterns were far more variable, with no single age group consistently at highest risk across countries. Pandemic preparations should not assume that young adults will necessarily be at particular risk when new flu viruses emerge, the authors argue.
The analysis also highlights substantial differences between populations within the same pandemic. Even in 1918, where the young adult mortality peak was a common feature, mortality at younger and older ages varied considerably across countries. This variability underscores the dangers of generalising from evidence based on a small number of countries. Most prior research on age patterns of risk during influenza pandemics has been based on the United States and a handful of other countries. The new study considers a far broader range of countries and finds that looking primarily at the United States can be misleading.
“The unusually high mortality among young adults in 1918 has strongly shaped how we think about pandemic risk,” says Dr Andrea Tilstra. “But when we compare across countries and across later pandemics, we see much more variation in age patterns. That suggests we should be cautious about generalising from any single historical case.”
By taking a comparative, cross-national perspective, the study provides a more nuanced understanding of age-specific mortality in pandemics. The authors conclude that future pandemic preparedness should avoid simple assumptions about which age groups are most vulnerable and instead be guided by context-specific evidence.
“Our findings show that pandemic mortality patterns can vary substantially between outbreaks and across populations,” says Dr Steele. “At a time when parts of the world are scaling back pandemic preparedness efforts, these findings highlight why flexible, evidence-based planning remains so important.”
Study author Prof Elizabeth Wrigley-Field of the University of Minnesota adds, “The 1918 pandemic was so dramatic that it seems to have permanently shaped how research fields have understood pandemic risk. It’s time we put that pandemic back in context, as one out of many ways that a new flu virus can play out.”
You can read the full-text article here.
