Enhancing positive mood in older adults: implications for vaccine effectiveness

The influenza vaccine is less effective in older adults compared to their younger counterparts. At the same time, this population is more susceptible to contracting influenza, with more severe consequences, including higher rates of complications, hospitalisations, and deaths. There is an abundance of evidence demonstrating how psychological factors, such as stress, can influence and modulate immune function, including response to vaccinations. Recent work has extended this to other psychological factors, suggesting that mood, or affect, may also be linked to vaccine response, however the evidence here is much more limited. This thesis presents three inter-related pieces of research, which sought to build on this evidence base and contribute to our current understanding of the influence of mood on vaccinations. The ultimate aim of this research was to develop an intervention to enhance positive mood, with a view to enhancing the effectiveness of the influenza vaccination in the older adult population. First, the evidence surrounding the effectiveness of using participant-driven choice in interventions compared to ‘no-choice’ interventions was systematically reviewed. This review sought to investigate whether the integration of participant choice within an existing, previously trialled, positive mood intervention would maximise mood enhancement and thus the potential to enhance vaccine-specific antibody levels. The review found that whilst choice-interventions led to less drop-out and greater adherence, evidence for mood-related outcomes was unclear and warranted further investigation. Second, a randomised controlled clinical study (n=654) was conducted to investigate the effectiveness of the previously trialled fixed-content positive mood intervention, a new choice-based intervention, and usual care, in terms of enhancing positive mood. Vaccine response at four-weeks post-vaccination was assessed as a secondary outcome. Results showed that both the fixed-content and choice-based interventions significantly improved mood compared to usual care, however there were no significant differences between the two interventions. There were no significant differences between groups in terms of antibody levels at four weeks post-vaccination. Finally, a qualitative study using a thematic-content hybrid analysis approach was carried out with a selection of participants from the randomised trial, to assess participants’ perceptions of how the intervention may or may not have worked, and to identify ways in which both the intervention and study experience as a whole could be improved for a future trial implementing the optimised intervention. Analysis revealed that both interventions, as well as the overall study experience, were liked by participants, indicating that further optimisation may not be necessary. Additionally, several potential mechanisms underlying the relationship between the interventions and mood were identified. The research presented in this thesis has several important implications. Firstly, that the use of choice should be considered where there is concern regarding drop-out or adherence, but may not be more effective than no-choice interventions in enhancing mood. Secondly, that brief positive mood interventions are effective in enhancing positive mood in older adults in a primary care setting. Future work is required to evaluate their impact on immune outcomes including mechanistic work to understand the relationship between mood and immunity, and a large scale trial, with immune response as the primary outcome