With flu season nearly upon us, a new study looks at the factors behind the extremely high mortality of the 1918 flu pandemic and how to prepare for future outbreaks. The authors warn that while the world is better prepared than 100 years ago, new challenges will affect the impact of the next influenza virus pandemic — including changing population demographics, antibiotic resistance and climate change.

This year marks the centenary of the 1918 influenza pandemic, the worst flu outbreak in recorded history. A new study into the human, viral and societal factors behind its severity provides valuable lessons that could save lives in future pandemics.

Publishing in Frontiers in Cellular and Infection Microbiology, the authors warn that while the world is better prepared than 100 years ago, new challenges will affect the impact of the next influenza virus pandemic — including changing population demographics, antibiotic resistance and climate change.

"We've seen three additional influenza pandemics since 1918: the 1957 'Asian' flu, the 1968 'Hong Kong' flu and the 2009 'swine' flu. Although milder than the 1918 pandemic, these highlights the constant threat that influenza virus poses to human health," says University of Melbourne Professor Katherine Kedzierska. 

"Like the 1918 pandemic, the severity of any future outbreak will result from a complex interplay between viral, host and societal factors," adds the Doherty Institute's Dr. Carolien van de Sandt. "Understanding these factors is vital for influenza pandemic preparedness."

Influenza Pandemic 

The 1918 influenza pandemic infected a third of the world's population and killed 50 million people. However, many people managed to survive a severe infection and others displayed only mild symptoms.

One explanation for the pandemic's severity is the viral strain itself. Some studies show the 1918 virus could spread to other tissues beyond the respiratory tract, resulting in more widespread damage. In addition, the virus had mutations that allowed it to be more easily transmitted between humans.

The authors identify public health as another important factor. In 1918, people suffering from malnutrition and underlying diseases, such as tuberculosis, were more likely to die from the infection.

This is still relevant today: climate change could result in crop losses and malnutrition while increasing antibiotic resistance could see bacterial infections becoming more prevalent. Future pandemics will also face the challenge of obesity, which increases the risk of dying from influenza.

Future Pandemic 

Population demographics also play a role. Strangely, one of the most severely affected groups in 1918 was one that is usually resilient — young adults. The researchers think older people may have been spared due to previous exposure to other viruses, giving them greater immunity to the 1918 viral strains. However, given that seasonal flu typically kills the very old, today's aging population will likely be another challenge in any future pandemic.

The researchers also report that basic methods to reduce disease transmission, such as banning public gatherings and hand washing, helped to reduce levels of infection and death during the 1918 pandemic — but only when they were applied early and for the entire duration of the pandemic.

"Until a broadly-protective vaccine is available, governments must inform the public on what to expect and how to act during a pandemic," says van de Sandt. "An important lesson from the 1918 influenza pandemic is that a well-prepared public response can save many lives."