Reduced Infectivity of Cold-Adapted Influenza A H1N1 Viruses in the Elderly: Correlation with Serum and Local Antibodies

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Abstract
To compare young and elderly adults in terms of their immune responses and rates of infection following intranasal vaccination with a live attenuated influenza virus. Time series, comparing outcomes in young and elderly convenience sample. Retrospective laboratory analysis of serum and nasal wash specimens collected during prior studies in which young or elderly volunteers had been inoculated with cold-adapted influenza A/Kawasaki/86 (H1N1) reassortant virus. Johns Hopkins Center for Immunization Research. Healthy young and elderly adults with pre-vaccination serum hemagglutination inhibition (HAI) antibody titers less than or equal to 1:8. Antibody responses in serum and nasal washes. The proportion of vaccinees who developed any serum or local antibody response was higher in young compared with elderly subjects (20/20 vs 5/14, P less than 0.0005). Resistance to infection with cold-adapted virus correlated with pre-vaccination levels of serum immunoglobulin G (IgG), serum IgA, and nasal wash IgA antibody to whole virus antigen. Age was highly correlated with a lack of response to vaccine by simple regression, but not when data were adjusted for pre-existing antibody levels. Cold-adapted reassortant influenza A H1N1 viruses achieve lower rates of infection in elderly than young adults, primarily due to age-related differences in preexisting levels of immunity which may not be reflected by HAI titer.

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