Dose-dependent antibody response to influenza H1N1 vaccine component in elderly nursing home patients.

The effects of an increased antigen dose on HI, IgG, IgA, and IgM antibody responses to influenza A/Taiwan/1/86 (H1N1) were investigated in 92 elderly nursing-home residents (mean age 81 years) and 104 young subjects (mean age 20 years). At a standard 10-microg dose, HI and IgG titer rises were lower in the elderly. HI titers did not improve at higher vaccine dosages. By contrast, influenza-specific IgG and IgA antibody responses were dose dependent in elderly subjects, but not in young. In the young subjects, IgM antibody responses were dose dependent. The improved antibody responses in the elderly as observed in IgG and IgA were not reflected in the HI response. Therefore, the evaluation of antibody production by HI only may lead to an underestimate of the immune response in elderly people.