"This suggests that the flu vaccine doesn't protect seniors as much as has been thought," said Michael L. Jackson, PhD, MPH, a postdoctoral fellow at the Group Health Center for Health Studies. "Ours is by far the largest case-control study of flu vaccine in the elderly."

This kind of study compares cases with controls. The cases were patients with community-acquired pneumonia treated in a hospital or elsewhere. The controls were people matched to cases by sex and age but with no pneumonia. Both groups were found to have similar rates of flu vaccination after adjusting for confounding effects of other diseases. All had intact immune systems and none lived in a nursing home.

Jackson and his colleagues carefully reviewed medical records to reveal details of seniors' health and ability to do daily activities.

"We tried to overcome the limits of previous studies done by others," Jackson explained. "Those studies may have over-estimated the benefits of the flu vaccine in the elderly for various reasons."

For instance, those studies looked only at pneumonia cases treated in a hospital. They also included seniors who had immune problems, which limit potential benefit from vaccination. And they didn't review medical records to get information on chronic diseases, such as heart or lung disease, which raise the risk of pneumonia.

Most importantly, those previous studies also failed to account for differences between healthier seniors and those who were frail, Jackson said. Frail seniors are older and have chronic diseases and difficulty walking.

They are less likely than younger, healthier seniors to go out and get vaccinated — and more apt to develop pneumonia," he said.

Pneumonia is a common and potentially life-threatening complication of the flu, Jackson said. But pneumonia can happen without the flu. "That's why our study used a control time period, after flu vaccine became available but before each flu season actually started," he said.

During those pre-flu-season periods, people who had been vaccinated were much less likely to get pneumonia. Why? "Because those who got the vaccine happened to be healthier — not because the flu vaccine was protecting them from pneumonia caused by the flu, since it wasn't present yet," he explained.

"Despite our findings, and even though immune responses are known to decline with age, I still want my grandmother to keep getting the flu vaccine," said Jackson. "The flu vaccine is safe. So it seems worth getting, even if it might lower the risk of pneumonia and death only slightly."

Jackson's co-author Lisa A. Jackson, MD, MPH (no relation), a senior investigator at the Group Health Center for Health Studies, agreed. "People age 65 and older should still get yearly flu vaccines as usual." But she said researchers should work to better understand how well the current flu vaccines work in seniors — and to explore other options for controlling flu in the "old old." Examples include administering bigger doses or stronger types of vaccines and conducting randomized, controlled trials comparing them.

Additional co-authors are Group Health's Jennifer C. Nelson, PhD, and William Barlow, PhD; Noel S. Weiss, MD, DrPH, of the Fred Hutchinson Cancer Research Center and University of Washington; and Kathleen M. Neuzil, MD, MPH, of the Program for Appropriate Technology in Health (PATH), University of Washington, and the Group Health Center for Health Studies. A fellowship grant from the Group Health Foundation and internal funds from the Group Health Center for Health Studies funded this study.

Note: If no author is given, the source is cited instead.

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