Influenza: The Common Virus That Can Kill
What Is Influenza?

Influenza is a viral attack on your respiratory system. It invades lung cells and makes you feel extremely weak, tired, achy, feverish, and congested. An influenza infection can sometimes produce vomiting, diarrhea, and other symptoms. The influenza virus causes a very specific illness but is sometimes blamed for other diseases with flulike symptoms, especially fever, vomiting, and diarrhea. Since the virus attacks only the lungs, there’s no such thing as “stomach flu.” That misleading term covers a number of ailments caused by nonflu viruses, bacteria, and parasites.

The great majority of infected people fight off the virus and recover within a couple of weeks. But virus strains change each season, which means people who recover can’t become immune to the flu, as they do to a chickenpox virus, for example. They build resistance only to the very specific strain that infected their bodies, and this strain might not even exist the following flu season. People can come down with the flu many times over the course of a lifetime.

According to WHO, in less than 1% of cases a seasonal flu virus kills its host or weakens the body enough to allow other diseases such as pneumonia to cause death. People over the age of 65 and having existing health problems account for more than 90% of seasonal flu deaths, even though more young children usually catch the flu than any other group.

In a shocking and still partly unexplained exception, the virus strain that caused the 1918 Spanish flu pandemic specialized in killing young and healthy teens and adults. Within days their skin turned blue, their lungs filled with fluid, and they died abruptly, sometimes drowning in their own lung fluids.

	Digging Deeper Is it a cold or the flu?

The 2009 H1N1 global outbreak proved to be no more deadly than most seasonal influenza viruses, although like the 1918 pandemic there was a larger proportion of deaths in younger people than for seasonal flu.

A closer look at the structure of the influenza virus shows why this common germ spreads so easily and how it can turn into a killer.