Poster Presentations

Session Title: VACCINE AND PREVENTION

EXPERIMENTALLY MODELLING IMMUNISATION DECISIONS: THE EFFECTS OF DISEASE, VACCINE REACTION AND HEALTH PROFESSIONAL FACTORS

K. Brown¹, A. Murphy¹, J. Green², M. Hudson³, J.S. Kroll⁴, M. Ramsay⁵, G. Fraser⁶, N. Sevdalis^1
1Clinical Safety Research Unit, Imperial College London, ²Department of Adult Psychology, Central and North-West London NHS Foundation Trust, London, ³Centre for Emergency Preparedness and Response, Health Protection Agency, Wiltshire, ⁴Department of Paediatrics, Faculty of Medicine, Imperial College London, ⁵Centre for Infections, ⁶HPA London, Health Protection Agency, London, UK

Background and aims: Most studies describing factors influencing immunisation decisions do so in specific vaccine or disease contexts, where unmeasured context-specific covariates may influence findings. We investigated the mechanisms underlying these decisions in a “sterile” experimental situation - a vital step before working with them in real-life.
Method: Participants imagined they were deciding whether to immunise their one-year-old child. In Study 1, disease and vaccine reaction likelihoods were presented; in Study 2, disease and vaccine reaction severity; and in Study 3, health professional opinion, consulting style and trustworthiness; all using vignettes. Each of these factors had multiple levels, e.g. low/medium/high, and all possible combinations of levels within each study were presented (full-factorial design). For each vignette participants marked how likely they were to accept the vaccine based upon the information given, on a Likert scale (range 0-100%, 10% intervals).
Results: Over 150 London Psychology undergraduates completed questionnaires. Disease and vaccine reaction likelihood and severity significantly predicted intention to immunise, and there were significant interactions between these factors (higher intention when disease common and serious and vaccine reaction uncommon and mild), suggesting that participants were mentally engaging in cost-benefit analyses. Health professional input significantly predicted intention to immunise and interacted significantly with other factors.
Conclusions: These data suggest that immunisation decision-makers use multi-factor information logically and effectively. This study demonstrates the utility of a context-free experimental approach to unpack sensitive immunisation decisions, and provides rationale for exploring these mechanisms with parents in hypothetical situations and validating the model in real situations.