1580 influenza pandemic

The earliest pandemic that can definitely be attributed to flu occurred in 1580. It began in Asia, spread to Africa and then hit Europe. It left entire Spanish cities depopulated and killed 8,000 people in Rome. The outbreaks in Italy led directly to the name of the illness. "Influenza" comes from the Italian phrase Influenza del Freddo, or "influence of the cold". However, the word would not appear in the English language for another 160 years.

1830-1848 influenza pandemic

There were four outbreaks during this period. An epidemic in 1830-1831 may have originated in China. Then, in 1833, influenza advanced west out of Russia into greater Europe. In 1836-1837, the spread of the illness moved mainly from north to south. Meanwhile, in 1847-1848 the disease swept through the Mediterranean to southern France and then elsewhere in Western Europe. Each of the four epidemics spread rapidly, causing high morbidity rates. Although case-mortality rates were low, each epidemic killed thousands, with most deaths occurring among the elderly.

1918 Spanish flu

The Spanish flu of 1918 is recognized as history's worst epidemic. It is estimated to have infected 50 percent of the global population and killed 20 million to 40 million people. The disease killed more people in a single year than bubonic plague over the entire four-year course of the Black Death. Spanish flu affected young, healthy adults more than the elderly and the sick. This is because the viral strain caused a cytokine storm, or fatal immune reaction, which led to the immune system destroying the body. Strong immune systems were affected more, as in the case of healthy, young adults. Children and the elderly, who had comparatively weaker immune systems, were not affected as badly.

2009 flu pandemic

The first cases of a new type of swine flu were reported in California and Texas in March 2009. Subsequent genetic analysis suggests that the strain may have started circulating in humans in January the same year. On April 27, with 900 cases of suspected swine flu reported in Mexico, the World Health Organization upgraded the pandemic warning level from three to four on a six-point scale. Intensive efforts to understand the virus and develop a vaccine began immediately. On June 11, the WHO officially declared swine flu a pandemic. It resulted in 18,500 deaths.

Sources: Popular Science, World Health Organization, New Scientist, The Journal of Applied Microbiology

(China Daily 01/29/2013 page6)