Flu Vaccine Has Dramatic Effect on Older Adults' Health

What if you were told there was a safe and free annual treatment that could significantly decrease your risk of being hospitalized for heart disease, stroke, or pneumonia and even reduce your risk of dying by 50%? You might laugh and assume that such a thing is impossible. But for adults over 65 years of age, that treatment is not just a promise that is years away from becoming reality. It has been available for decades and is even fully covered by Medicare: it's called a flu shot.

Over the years, numerous small studies have found links between influenza and rates of hospitalization for respiratory illness, heart disease, and stroke. Recently, a large observational study, published in the New England Journal of Medicine in April 2003, tested the effect of the influenza vaccine on these outcomes in the elderly. Dr. Kristin Nichol, Chief of Medicine at the Minneapolis Veterans Affairs Medical Center, and colleagues studied nearly 300,000 persons over 65 years of age over the 1998-99 and 1999-2000 flu seasons. They found that study participants who received flu shots were about 20% less likely to be hospitalized for heart disease or stroke, about 30% less likely to be hospitalized for pneumonia or the flu, and 50% less likely to die for any reason during flu season.

Although Dr. Nichol and her team were expecting positive results based on previous studies, she said they were still "astounded" to see a simple vaccination providing such dramatic results. "This is a greater health benefit than almost anything else in medicine over such a short period of time," she explains. "I am usually reluctant to make particularly strong claims on the basis of an observational study, even one of this size, but other studies have also shown a reduction in mortality. This study doesn't stand alone, and that lends even more confidence to the findings."

Scientists are not yet sure why the flu shot has such remarkable effects on the health of older persons. It likely prevents pneumonia and other respiratory problems by preventing the development of influenza, which can leave the lungs of elderly patients vulnerable to secondary infections and complications. As for the shot's reduction in the rates of hospitalization for heart disease and stroke, Dr. Nichol speculates that by preventing the flu, the vaccine is preventing a cascade of inflammatory responses produced by the immune system. These inflammatory changes may promote blood clots or harm blood vessel walls. "This study definitely establishes substantial associations between the flu and cardiovascular diseases," says Dr. Nichol. "It can help to support the generation of hypotheses on underlying biological mechanisms. As lab-based researchers investigate these mechanisms, we might also learn other things about preventing and treating influenza and its complications."

Dr. Nichol hopes her work can help increase vaccination rates among the elderly, which have plateaued in recent years at under 70%. This falls well short of the 90% vaccination rate the U.S. government hopes to achieve among senior citizens by the year 2010. "Anything we can do to help light a fire, to create a sense of urgency and real benefit, is worthwhile," says Dr. Nichol. "With this extremely inexpensive and safe intervention, we can keep people out of the hospital, and we can prevent them from dying. People should get really excited about these results."

Reviewed: September 3, 2003
Published: September 5, 2003