ObjectiveInfluenza and pneumonia account for significant morbidity and mortality, particularly in older individuals. Previous studies have shown that spousal caregivers of patients with dementia have poorer antibody and virus specific T cell responses to an influenza virus vaccine relative to noncaregiving control subjects. This study tested the hypothesis that stress can also significantly inhibit the IgG antibody response to a pneumococcal bacterial vaccine.MethodWe measured antibody titers of current caregivers, former caregivers, and control subjects after vaccination with a pneumococcal bacterial vaccine.ResultsCaregivers showed deficits relative to controls and former caregivers in their antibody responses to vaccination. Although the groups did not differ before vaccination or in the rise in antibody 2 weeks or 1 month after vaccination, current caregivers had lower antibody titers 3 and 6 months after vaccination than either former caregivers or controls.ConclusionsThese data, the first evidence that chronic stress can inhibit the stability of the IgG antibody response to a bacterial vaccine for pneumonia, provide additional evidence of health risks associated with dementia caregiving.