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a Eastern Virginia Medical School, Glennan Center for Geriatrics and Gerontology, Norfolk
Janet E. McElhaney, Glennan Center for Geriatrics and Gerontology, Eastern Virginia Medical School, 825 Fairfax Avenue, Suite 201, Norfolk, VA 23507 E-mail: Mcelhaje{at}evms.edu.
CURRENT influenza vaccines are 50% to 60% effective for preventing serious illness in older people but may be limited in persons with poor health, particularly in the institutional setting (1). Poor nutritional status occurs commonly in older persons (2)(3). Improving nutritional status may be one strategy for enhancing the response to influenza vaccination in older adults. Thus, in mice, Han and colleagues (4) showed that a vitamin E supplement would reduce influenza viral titers during an infection and decrease the anorexia and weight loss produced by influenza. Pollett and colleagues (5) showed that protein-deprived mice had reduced IgM antibody response to intranasal influenza infection. Chandra and Puri (6) found that, in humans, nutritional support improved the antibody response to influenza virus. In contrast, Pozzetto and colleagues (7) reported no relationship of protein status to postvaccinal antibody response to influenza viruses in older humans.
This month in the Journal, the article by Wouters-Wesseling and colleagues (8) reports that a nutritional supplement, including calories, vitamins, and minerals, showed a potential benefit due to improved antibody responses to influenza vaccination. These results add to previous studies that have compared nutritional markers or effects of nutritional supplements on the immune response to influenza vaccination in both the community and institutional settings. A review of these studies reveals mixed results that may be due to differences in study groups with respect to sample size or heterogeneity of health and vaccination history, all of which contribute to the variability of the immunologic responses measured.
Complicated interactions between various vitamins and minerals and specific deficiencies related to chronic disease states may account for study-to-study differences in results. Moreover, the benefit of supplementation may only be observed when a nutritional deficiency is reversed. Thus, study populations may need to be characterized according to underlying chronic disease, the extent of disability, and the associated nutritional deficiencies for that subset of older people. Smaller studies for hypothesis generation and collection of pilot data may be feasible in these well-defined groups of older people. Studies that do not include careful measurement of health indicators including nutritional status may require very large study groups (in excess of 700) to adequately power studies, particularly in the institutional setting (9)(10).
The most commonly used assay for measuring antibody titers to influenza is the hemagglutination inhibition assay. Analyzing for differences in seroconversion rates or mean fold increase in antibody titers following vaccination may not be a valid comparison in repeatedly vaccinated older people. Even though the absolute postvaccination titer is protective, vaccination from the previous year may increase prevaccination titers and diminish the fold increase in antibody titer. The fact that older adults who are vaccinated on an annual basis receive better protection from the vaccine compared to first-time vaccinees suggests that the absolute postvaccination titer is a better surrogate of protection than the mean fold increase. Seroconversion (four-fold rise in antibody titer) or seroprotection (postvaccination titer greater than or equal to 40) should be considered equivalent measures of the response rates to vaccination. This type of analysis may have yielded different results in the article by Wouters-Wesseling and colleagues and may account for some of the inconsistent results reported in the literature.
Antibody titers measure only the humoral component of the immune response to influenza and do not measure the cellular immune response, which may be more important in older people. Assays of T-cell responses to influenza stimulation are more labor intensive and need to be applied to smaller groups of well-characterized subjects, including specific nutritional indices to limit the variability of the immunologic responses within study groups. In healthy older adults, age-related changes in humoral and cytokine responses cannot be explained on the basis of vitamin and mineral levels (11). In contrast, the article by Kohut and colleagues (12) reports that the level of exercise activity, vitamin supplements, and life-related stressors among healthy older adults are associated with differences in antibody and cytokine levels following vaccination. Identification of the reversible deficits in immune function related to age and chronic disease may be the necessary link to developing the appropriate "biopsychosocial" supplement that improves immune response to influenza vaccination in older adults.
Received April 1, 2002
Accepted April 1, 2002
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This article has been cited by other articles:
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  J. E. Morley Anorexia and Weight Loss in Older Persons J. Gerontol. A Biol. Sci. Med. Sci., February 1, 2003; 58(2): M131 - 137. [Full Text] [PDF]
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J. E. Morley Editorial: Hot Topics in Geriatrics J. Gerontol. A Biol. Sci. Med. Sci., January 1, 2003; 58(1): M30 - 36. [Full Text] [PDF]
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