When the first cases of a mysterious flu came to light in 2009, the disease was dubbed "swine flu." Now, researchers understand that we're dealing with a completely new monster of a virus, and historic instances of pandemic flu loom large in public health officials' minds. The scenario that no one wants to repeat is the deadly 1918 flu, sometimes called Spanish flu. This disease was also originally attributed to swine, though now the birds get the blame. Within a year, more than 50 million people died; 500,000 of those fatalities were in the United States alone [source: Beck].
It's still possible that the current H1N1 virus, though mild now, could mutate into a deadlier flu. However, just as the virus could develop into something much deadlier, it could also go the other way and become milder as it travels the world. If that happens, it would be something of a repeat of 1976, the last time swine flu broke out in the United States.
That year, two soldiers at Fort Dix came down with the flu, and one of the men died. Fearing another deadly epidemic, the government announced plans to vaccinate the entire country. However, the disease never spread beyond Fort Dix, and the vaccine, which was never explained well to the public, was linked to a paralyzing neuromuscular disorder known as Guillain-Barre syndrome [source: Di Justo]. It's understandable that people who remember the events of 1976 are wary of the panic surrounding the new pandemic. (Those who were vaccinated in 1976 should take note that they're not protected from the 2009 version of swine flu.)
Right now, no one knows whether the current virus will be immensely fatal or just a big fizzle. But there's one thing in particular about each of these outbreaks to note: In each case, the deaths occurred in people that we'd otherwise consider young and healthy. We tend to think of flu resulting in the deaths of the very old and the very young, and the pandemics did affect those age groups. But the soldier at Fort Dix was a young man likely in very good physical condition, and more than half of the serious cases of the 2009 swine flu have involved people aged 5 to 24. For that reason alone, we have reason to remain vigilant about H1N1. So what, exactly, are we supposed to be on the lookout for?