'Weakened' immunity of caregivers

“Caring for children with developmental problems such as autism or Down's syndrome can weaken parents' immune systems,” BBC News reported. It said that a study has shown that carers of children with developmental disabilities had less of an immune response when injected with a pneumonia vaccine than those who had children without such difficulties. The researchers had said the reduced immune response was likely to be caused by stress related to providing round-the-clock care.

This study compared the immune response to a pneumonia vaccine in parents of developmentally disabled children and parents of normally developing children. It found the immune response of parents with developmentally disabled children appeared to be poorer. It seems plausible that this sort of caregiving can affect parental health, and this study appears to demonstrate this in response to vaccination. Further studies are needed to investigate the possible reasons behind this, to see whether there are demonstrable effects in other areas of health, and to determine what can be done to maintain the health of caregivers.

Where did the story come from?

Dr Stephen Gallagher and colleagues from the University of Birmingham carried out the research. Funding sources were not given. The article is currently in press (and available electronically) in the peer-reviewed medical journal, Brain, Behaviour, and Immunity.

What kind of scientific study was this?

In this non-randomised controlled study, the researchers were interested in whether the parents of children with developmental disabilities would have a diminished immune response to a pneumonia vaccine. They invited the parents of 32 children with developmental disabilities (autistic spectrum disorders and Down’s syndrome) and the parents of 29 children who were developing normally to three testing sessions. The parents were recruited through support groups, advertisements in newsletters, local schools and through invitations distributed through associations. The children were aged between 3 -19 years of age, and were living at home during the school term and attending ‘special needs’ schools, or receiving support within a mainstream school.

During the first session, the parents completed questionnaires and gave blood samples. The questionnaires assessed levels of parental depression, stress, social support, caregiver burden, problem behaviour in the child, sleep quality, health behaviours, and time spent caregiving. The pneumococcal vaccine was given to the parents via injection into the arm at this first meeting. They were invited to return one month and six months later to provide further blood samples. The blood was used to determine the level of pneumococcal antibodies, thereby indicating the body’s response to vaccination.

The researchers compared the response of parents of children with development disabilities to parents of normally developing children, taking into account other factors that may have affected this (including sleep quality, health behaviours, etc). The researchers defined a ‘response’ to the vaccine as a two-fold increase in antibody levels. The number of ‘responders’ in each parent group was then compared.

What were the results of the study?

After taking into account the parents’ antibody levels before vaccination, the study found that those who cared for the disabled children had a poorer response to the vaccine than the group of parents of normally developing children.

After a month, the number of ‘non-responders’ to the vaccine was 4% in the group of parents of normally developing children compared to 20% in the group of parents of disabled children. After six months, the number of non-responders stayed the same amongst the parents of the normally developing children, but rose to 48% in the group of parents with disabled children. These differences were not affected by parental smoking, diet, exercise, or alcohol consumption. They also did not change when the researchers took into account the parent’s age, their work outside the home, time spent caregiving, sleep quality, depression, perceived stress, social support, or ‘caregiver burden’(parent-reported). However, child problem behaviour (rated by parents) played a significant part in the antibody response to vaccination.

What interpretations did the researchers draw from these results?

The researchers say that their study has found that parents who care for children with development disabilities show a poorer response to a pneumococcal vaccine than the parents of normally developing children. Behavioural characteristics “of the care recipients may be a key determinant of whether or not immunity is compromised in this context”.

What does the NHS Knowledge Service make of this study?

Although the researchers call this study a ‘prospective case-control study’, it is not a case-control study by the usual definition (i.e. where participants are chosen on the basis of their outcome; in this case it would be whether or not the parents responded to the vaccination). A more accurate description would be to call it a non-randomised, controlled trial. The study has the following limitations, which the researchers discuss:

• The parents of disabled children were recruited through support groups. This could have introduced bias as these parents could have been more ‘stressed’ than the average parent carer.
• This was a small study with a small number of participants (though the researchers address this by stating that it was not much smaller than other studies on this subject).
• The researchers raise the possibility that other factors could have been responsible for the observed differences. However, they point out that their analysis took into account many of the obvious ones.
• Of the factors that they did consider, the researchers state that child behavioural problems – particularly conduct problems – were largely responsible for the difference in response to vaccine between the two parent groups at month 1 (but not at month 6). The link between childhood behaviour and immune response is a complex one, and the results here suggest that it ‘mediates’ the link between whether a parent is a carer or not and how they respond to the vaccine, i.e. there is unlikely to be a direct causal link between caregiving and poor immunity.

Although this small study has its limitations, the results suggest that parents of children with developmental disabilities may have a poorer immune response as judged by their response to vaccination. It is plausible that round-the-clock care for a developmentally disabled child is stressful, and that this stress can have an impact on the caregiver’s health.

More research is needed to determine whether this means real-life differences in rates of illness between parental groups. The researchers speculate that an underlying biological mechanism may be responsible for the differences here, and suggest that increased secretion of a stress hormone may be responsible for reduced immune response. However, further research is needed to clarify this.