When the Flu Is Taken Lightly. Influenza is a serious disease with a very high mortality. Influenza vaccination decreases the death rate, especially in the very young and those older than 65.

In an interview, Dr. Poland said he thought that the biggest barrier to more widespread inoculation was a false perception about the dangers of influenza.

"We call every respiratory and gastric illness in winter the flu," he said. "People think flu is a minor illness."

In reality, he said, "Influenza has a very distinct set of clinical symptoms, including the sudden onset of high fever and severe fatigue that literally drives people to bed."