This year is the 100th anniversary of the outbreak of the 1918 influenza pandemic (also known as Spanish flu). It was an unusually deadly influenza pandemic, the first of the two pandemics involving the H1N1 influenza virus. It infected 500 million people around the world, including remote Pacific islands and the Arctic, and resulted in the deaths of 50–100 million people, making it one of the deadliest natural disasters in human history.
Most influenza outbreaks disproportionately kill juvenile, elderly or already weakened patients; in contrast, the 1918 pandemic predominantly killed previously healthy young adults. Several possible explanations exist for the high mortality rate of the 1918 pandemic. Some research suggests that the specific variant of the virus had an unusually aggressive nature. One group of researchers recovered the virus from the bodies of frozen victims, and found that transfection in animals caused a rapid, progressive respiratory failure and death through an over-reaction of the body's immune system. It was then postulated that the strong immune reactions of young adults ravaged the body, whereas the weaker immune systems of children and middle-aged adults resulted in fewer deaths among those groups.
Influenza will be a topic of an article in a future issue of Pathology in Practice.