Chronic stressors such as caregiving have been associated with reduced antibody production after vaccination and elevated interleukin (IL)-6 in older adults. However, individual differences in repetitive thought, that is, frequent or prolonged thought about oneself and one's world, can modify perception and effects of stress. For example, worry during stressful circumstances has been associated with poorer immune outcomes, whereas cognitive processing has been associated with better outcomes. The present study tested the relationship of caregiving and two types of repetitive thought, negative (e.g., worry) and neutral (e.g., reflection), to pre- and post-influenza vaccine antibody and IL-6. Dementia caregivers (n=14) and controls (n=30) were interviewed and had blood drawn pre- and post-vaccine in a multi-wave study. Multi-level models found that caregivers had higher IL-6 than controls after vaccination (t(23)=2.36, p<.05). There were several interactions between caregiver status and repetitive thought in predicting both depression and immune responses to vaccination. Among caregivers, negative repetitive thought predicted more depression and lower antibody titers, whereas neutral repetitive thought predicted less depression and higher antibody titers, but also higher post-vaccination IL-6. Among controls, negative repetitive thought predicted more depression but higher antibody titers, whereas neutral repetitive thought predicted less depression and lower post-vaccination IL-6. In mediational tests, depression did not account for the effects of repetitive thought. Results generally support beneficial effects of neutral repetitive thought and detrimental effects of negative repetitive thought, but those effects may be reduced or even reversed depending on life circumstances.