Background: There are many reports of psychological morbidity in spousal carers of patients with dementia. The consequences of this increased stress on the immune system are unclear. We investigated whether antibody responses to influenza vaccination differed between carers and a control group, and the relation of the antibody response to the hypothalamic-pituitary-adrenal (HPA) axis.
Methods: 50 spousal carers of dementia patients, median age 73 years (IQR 66-77), and 67 controls (68 years [66-71]) of similar socioeconomic status were enrolled. Anxiety and depression were measured by the Savage Aged Personality Screening Scale and stress by the Global Measure of Perceived Stress scale. Principal-component analysis was used to yield a summary score of emotional distress from these two scales. Salivary cortisol concentrations were measured over a single day at three times (0800-1000, 1100-1300, and 2000-2200). Participants received a trivalent influenza vaccine and IgG antibody titres to each strain were measured on days 0, 7, 14, and 28.
Findings: Mean scores of emotional distress were significantly higher in carers at each time point than in controls (all p<0.0003). Mean (SD) salivary cortisol concentrations, calculated as area under the curve (AUC), were higher in carers than controls at all three assessments (6 months 16.0 [8.0] vs 11.2 [4.4], p=0.0001; respectively). Eight (16%) of 50 carers and 26 (39%) of 67 controls had a four-fold increase in at least one of the IgG titres (p=0.007). There was an inverse relation between AUC cortisol and IgG antibody titre to the Nanchang strain that was significant on day 14 (r=-0.216, p=0.039).
Interpretation: Elderly carers of spouses with dementia have increased activation of the hypothalamic-pituitary-adrenal axis and a poor antibody response to influenza vaccine. Carers may be more vulnerable to infectious disease than the population of a similar age.