Immunity to influenza in the elderly.

Influenza is caused by a constantly varying segmented RNA virus that necessitates yearly review of vaccine composition. Humans over the age of 65 years are considered at high risk from influenza; during influenza epidemics the rate of hospitalization in the elderly is very high and up to 90% mortality can occur. Vaccination of the elderly has been shown to be efficacious and cost effective but immunological senescence in the institutionally confined frail elderly is demonstrated by failure to induce herd immunity after vaccination. Reductions in B- and T-cell immunity and in levels of interleukin-2 are age related. Attempts to increase the immunoresponsiveness of the elderly to influenza vaccines have given mixed results. The most convincing evidence is in rodents where dietary caloric restriction has been shown to enhance viral immunity.