After the first several weeks of uncertainty, most of the news about the 2009 H1N1 "swine flu" pandemic has been reassuring, according to the Harvard Health Letter, December, 2009 edition.

Much of that has to do with the nature of the H1N1 virus itself, which spreads easily and makes people sick, but so far rarely in a life-threatening way. And the word pandemic is misunderstood: a disease is considered pandemic if it has spread globally and affects a larger-than-usual proportion of the population. The disease needn't be severe.

But a major reason for the calm has been the measured public health response. Plenty of information has been made available (this is the first Internet-age pandemic). A vaccine was developed and put into production, although shortages are a serious concern. Health officials gave us simple, concrete things to do to protect ourselves and others: cough and sneeze into your sleeve, wash your hands often, get vaccinated with both the seasonal and H1N1 flu vaccines, stay home if you're feeling sick.

This wasn't the flu pandemic that the experts were expecting, according to the Harvard Health Letter. For years, they've eyed the H5N1 bird flu virus circulating in Asia to see if it would mutate and become transmissible among humans. Instead, H1N1 emerged in Mexico with a complicated quadruple pedigree: two strains of swine flu, a human strain, and a bird one.

Hospitalization and death rates from the new virus have been high in healthy young adults and quite low in people older than 60. One explanation for that pattern is that older people may have some immunity left over from exposure to a previous version of H1N1.

“We have months of flu season ahead of us,” says the Harvard Health Letter. “Much could go wrong. Flu viruses are more contagious and more likely to produce severe illness in cold, dry air. They can mutate. Still, early indications were that this pandemic will stay manageable. As expected, flu rates in the Southern Hemisphere returned to normal in the fall. When we went to press, the worldwide death toll was about 5,000 — a modest number, all things considered. And most Americans were going about their business, with cleaner hands than ever before.”