Past pandemics of influenza resulted from cross-infection of humans by the avian flu virus. In 1918, the most devastating pandemic, the infection resulted from a mutation in the virus; whereas, the other two smaller
pandemics occurred from a reassortment of the virus antigen. It is believed that pandemics occur decades after a shift in the antigen. This shifting was noticed in the 1970s, so there is concern that a pandemic is pending.
The most well-known and well-documented pandemic of influenza occurred in 1918, at the end of World War I. This pandemic, named The Spanish Flu, was responsible for up to 50 million deaths worldwide, most from influenzal pneumonia. Having lost many lives in the war, the flu further decimated the world’s population. Because of the impact on the population as well as the economy, this pandemic is still under review to understand what happened and how to prevent a similar pandemic.
Influenza was less understood in the early 20th century than it is now. Diagnosis was delayed and therefore, treatment was suboptimal to contain the disease. Once it was recognized and affected people were quarantined,the virus had already spread. The rapid rate of spread of this disease across the globe shows the high degree of virulence of this virus. This spread occurred despite the lack of mobility that exists today, which is a major concern for modern scientists.
Although we do have some protective measures with vaccines and antivirals, if the virus has mutated sufficiently to be resistant to both vaccine and treatment, a pandemic would be hard to control. The increase in mobility in the air, on ground and via sea will make it virtually impossible to control the spread of the virus once it takes hold.