An influenza virus has only eight genes — far fewer than the estimated 25,000 that human beings possess — but its simplicity hasn't stopped it from wreaking havoc on humanity for centuries. Even today, with vaccines and antivirals, normal seasonal influenza kills some 36,000 Americans each year. And every once in a while, it gets much worse. When new flu viruses arise and begin spreading easily, they can trigger global pandemics. Sometimes they're relatively mild, like the pandemics of 1957 and '68. But sometimes they can be as catastrophic as the Spanish flu of 1918, which killed as many as 100 million people.
We're living through a pandemic right now, but we don't yet know if the H1N1/09 virus — the new official name for what was first called swine flu — will sear the history books or merely strike us a glancing blow. In just a few months, H1N1/09 has spread to nearly every country in the world, infecting so many people that the World Health Organization has officially stopped counting. In nations where it is already winter, like Argentina, H1N1/09 has caused billions of dollars in damage, and China is quarantining foreigners suspected to have the flu. In the U.S., the virus has continued to multiply in the summer — a worrisome sign, since influenza usually takes a vacation when the weather improves.
Still, so far H1N1/09 hasn't proved a serious killer. But as the U.S. prepares for an uptick in infections this fall, even a mild pandemic could overload a clogged health-care system. And there's no guarantee the virus won't get worse — the Spanish flu was relatively light in the spring of 1918, only to turn lethal that autumn. U.S. health officials said on July 29 that they hope to have 120 million doses of a new H1N1/09 vaccine ready by October, but the virus could change by then, or the vaccine might prove less than effective. Virologists like to say the only thing predictable about influenza is its unpredictability. As the world waits for the next onslaught, that bears remembering.