Infectious disease experts are warning that flu can lead to an increased risk of heart attack, stroke and disability in elderly patients for months after they have recovered from their illness.

Evidence has been growing over the last several years about post-flu risks that most people and even some physicians don't know about, according to William Schaffner, MD, professor of Preventive Medicine and Infectious Disease at Vanderbilt University School of Medicine.

"We all know about the illness influenza causes, obviously fever and making you feel poorly, aches and pains, and that is because it sets up a systemic inflammatory response," Schaffner said.

"Not as well known, in the two weeks to a month after you recover from influenza you have a 3-5 times increased risk of having a heart attack. You have a 2-3 times increased risk of having a stroke. Nobody wants a heart attack or a stroke, so by preventing flu you prevent this inflammatory response and you can help prevent those strokes and heart attacks."

Older adults account for more than half of hospitalizations due to influenza and over 80 percent of deaths associated with influenza so there is an increased focus to make sure that they get vaccinated, Schaffner said.

"We have a couple of vaccines now that are particularly designed and licensed for use in older adults and that is because they produce an enhanced immune response in this population," he said.

Schaffner said the high-dose influenza vaccine is effective in older adults with four times as much vaccine as the normal vaccine. A second vaccine for the elderly was licensed for the first time last year and has an adjuvant.

"Both of those vaccines produce an enhanced immune response, and the data supporting that they prevent more influenza in older adults are really quite solid," Schaffner said.

The influenza virus can oftentimes have a domino effect in the elderly, leading to disability and decreased quality of life.

"Older people worry about becoming disabled and not being able to do the activities of daily living," Schaffner said.

"Influenza can take a person who is functional in society and make them very sick, but after they recover they may never get back to that same level of function that they had before. So flu can be like that first domino falling and beginning to push patients down the disability scale."