No discussion of the need for a flu shot would be complete without mention of the 1918-19 Influenza Pandemic. It infected 500 million people and caused deaths of an estimated 50 to 100 million (up to five percent of the world's population). Life expectancy plummeted by about 12 years during this period. More soldiers were killed by the flu than by wartime hostilities. Virtually every family on the planet, likely including your own forebears, was visited by this scourge. It was one of the great die-offs in human history, certainly unparalleled in modern times.
Because it is sometimes referred to as the “Spanish flu” (except in Spain, where it was known as “the Naples Soldier”), some people may assume that this epidemic was a special case, or that the disease was caused by an entirely different microbe from the flu we get vaccinated for each autumn. They would be wrong. Reports of the illness in countries involved in the War (Germany, Britain, France, and the United States) were censored to avoid undermining morale, but the press was free to write about what was happening in neutral Spain (the king was severely stricken, for example), giving the false impression that Spain was somehow the epicenter of the disease. In fact the disease struck everywhere, even in the remotest corners of the world.
Although like all flu outbreaks this one had some unusual features - in particular, its extremely high mortality rate and its disproportionate impact on previously healthy young adults - these phenomena can probably be explained in large part by the major humanitarian crises associated with World War I (widespread displacement, malnutrition, overcrowded medical camps and hospitals, poor hygiene), which not only facilitated spread of the virus but also increased susceptibility to secondary bacterial infections like pneumonia. Evidence on whether the strain that caused the disease was even particularly virulent in and of itself is mixed - though it may have taken awhile for the bug to find the right formula for propagating itself without killing off its host entirely.
In short, there is no evidence that the H1N1 influenza virus that caused the pandemic was qualitatively different than the ones we experience today. Nor was it qualitatively different from earlier flu outbreaks ("simply the same old grip," as one contemporary newspaper account put it). Nor is there any reason to think we are not doomed to repeat history if we ignore it. Indeed, lesser but still serious global flu epidemics have struck several times since 1918, including in 1957-58, in 1968-69, and in 2009-10, the so-called “swine flu” in which 12,000 Americans perished. Were they not overshadowed by the 1918 pandemic, these outbreaks might claim an even more prominent place in the history of human catastrophes than they already do.
In 1918 there was little that could be done to treat the disease or prevent its spread. Wearing masks, avoiding handshakes, and staggering work shifts to avoid overcrowding in the subways as was ordered by the New York City Health Commissioner were all tried to little avail. Luckily, we now have an effective vaccine against the flu and a government committed to annual forecasts and updates. The best prevention on both the personal and societal levels continues to be annual flu vaccination for everyone except individuals in a few special risk categories as outlined in my most recent post. Suggesting otherwise is beyond irresponsible.