The investigators recently conducted a longitudinal observational cohort study of multiple psychological (positive affect, negative affect, stress) and behavioural (physical activity, sleep, diet) influences on short and long-term antibody responses to influenza vaccination in older adults. This identified positive affect as the most influential psycho-behavioural factor on influenza-specific antibody responses, independently predicting both short and long-term antibody responses in the weakest immunogenic strain above and beyond known demographic and clinical determinants. Intriguingly, the investigators also observed preliminary evidence that positive affect on the day of vaccination was more predictive of antibody responses following vaccination than mood measured over the longer period surrounding vaccination. As influenza-specific antibodies are a well-established correlate of protection from serologically and clinically diagnosed influenza incidence, these data suggest that increasing positive affect immediately prior to vaccination could be used as a non-pharmacological vaccine adjuvant.