William Thompson, an epidemiologist with the Centers for Disease Control and Prevention in Atlanta, and colleagues developed a statistical model based on actual surveillance of disease cases, yearly monitoring of flu virus types and population figures to calculate fatalities from the flu and related illnesses in the last quarter of the 20th century.

Using an admittedly broad-brush approach, the researchers came up with an average annual toll of between 50,000 and 70,000 flu deaths in the United States, about twice as high as the average 20,000 to 40,000 deaths normally cited for a flu season by the CDC.

Both an aging population and an attempt to calculate flu's effects on a wide range of other illnesses that victims already had are responsible for the higher estimates.

"Between 1976 and 1999, the number of persons 85 years or older doubled in the United States. We found that persons in this age group were 16 times more likely to die of an influenza-associated, all-cause death than persons aged 65 to 69," said Thompson, lead author of the study. It is being published Wednesday in The Journal of the American Medical Association.

"Although it used to be whispered that influenza is 'the old man's friend,' it is hard to imagine anyone of any age choosing to 'befriend' it," noted Dr. David Morens, a flu specialist with the National Institute of Allergy and Infectious Diseases, commenting on the study in an editorial.

Flu experts note that many people succumb to a variety of conditions that are worsened by the flu, including long-standing heart and lung conditions, than directly from the virus.

For the 1976-77 flu season, the researchers calculated there were 16,263 influenza-associated deaths from all causes, although just 2,265 were directly caused by flu and pneumonia. By contrast, there were 68,328 "all-cause" flu-linked deaths in 1996-97, with 13,674 citing pneumonia and flu as the underlying cause.

Looking at data for the 1990s, the researchers noted that another virus - respiratory syncytial virus, known mainly as the source of lower and upper respiratory tract infections in young children - could be almost as dangerous to seniors as the flu.

"Although the importance of RSV among young children is well-known, we found that more than 78 percent of RSV-associated underlying respiratory and circulatory deaths occurred among people aged 65 years or older," the researchers said.

"This highlights the need for an effective RSV vaccine in both young children and elderly persons."

Although a vaccine against RSV is a high research priority, one is not yet available for children or adults. And though annual flu vaccination is strongly encouraged for the elderly every fall, millions still don't get the shot.

Many who get the shot have such weakened immune systems that the vaccine offers only limited protection from the illness, but still good protection from a severe or fatal case of the flu.