In older populations, caregiving for a spouse with dementia has been associated with a poor antibody response to vaccination. The present study examined whether younger caregivers, specifically the parents of children with developmental disabilities, would also show a diminished antibody response to vaccination. At baseline assessment, 30 parents of children with developmental disabilities and 29 parents of typically developing children completed standard measures of depression, perceived stress, social support, caregiver burden, and child problem behaviours. They also provided a blood sample and were then vaccinated with a pneumococcal polysaccharide vaccine. Further blood samples were taken at 1- and 6-month follow-ups. Caregivers mounted a poorer antibody response to vaccination than control parents at both follow-ups. This effect withstood adjustment for a number of possible confounders and appeared to be, at least in part, mediated by child problem behaviours. The negative impact of caregiving on antibody response to vaccination is not restricted to older spousal caregivers, but is also evident in younger parents caring for children with developmental disabilities. The behavioural characteristics of the care recipients may be a key consideration in whether or not immunity is compromised in this context