This study is a 2-arm, parallel, randomised controlled feasibility trial of a brief video intervention designed to induce positive affect (mood) in older adults in primary care settings prior to the receipt of influenza vaccination. Participants will be randomised into two conditions: experimental and active control. In the experimental condition, participants will view the approximately 15 minute long intervention video immediately prior to vaccination. In the active control condition, participants will view a matched video that is designed to be mood neutral. Pre-and-post positive affect levels will be assessed by self-report questionnaires. Immune response to the intervention and vaccination responses will be assessed in saliva and serum samples respectively.

The objectives of the study are to assess the impact of the intervention on mood, immune function, and antibody response to influenza vaccination in older adults. This feasibility trial will also allow data collection on exploring recruitment, attrition, intervention engagement, and practicality of collecting clinical data available through electronic records to inform the design of a future definitive trial.

The Centers for Disease Control (CDC) describe vaccinations as among the 10 most significant health achievements ever documented; and for many conditions they have been an unmitigated success (e.g., smallpox). There are, however, several populations in whom vaccine effectiveness is far from optimal. These populations are typically contending with underlying immune impairment by virtue of their advancing age and/or the presence of co-existing diseases (e.g., cancer). As a consequence, vaccines are most likely to fail those whom they most seek to benefit: individuals at the greatest risk of ill health.

This has prompted research into treatments that enhance immune function prior to vaccination, so called vaccine adjuvants. The aim of such treatments is to optimise the response the immune system makes to the vaccine antigens and, in so doing, increase the likelihood that the vaccine confers protection.

One area in which there has been interest is in the potential for developing psycho-behavioural vaccine adjuvants. There is considerable evidence that psychological and behavioural factors can modulate immunity; with diet, physical activity, stress, affect, sleep and social support all associated with immune response.

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.

Through a series of systematic steps, including focus groups and interviews with older adults and health care professionals, the investigators have recently developed a brief, positive affect intervention - designed to improve short-term mood in older adults and be deliverable within primary care. It is hoped this could act as a psycho-behavioural adjuvant to enhance poor responses to influenza vaccination in older adults. Before performing a definitive trial of the intervention's effectiveness, a feasibility trial is needed for number of reasons:

1. To assess whether our intervention can enhance positive affect (mood)
2. To collect information regarding likely recruitment, effect sizes, and attrition rates for informing the necessary size of a larger definitive trial
3. To examine the practicality and acceptability of delivering the intervention in routine primary care settings
4. To explore the feasibility of obtaining outcome data on healthcare usage for a large scale trial (hospitalisation, GP visits for flu-like symptoms from medical records)

In line with the above, the investigators will be conducting a 2-arm, parallel, randomised controlled feasibility trial of a brief video intervention designed to induce positive affect (mood) in older adults in primary care settings prior to the receipt of influenza vaccination. Participants will be randomised into two conditions: experimental and active control. In the experimental condition, participants will view the approximately 15 minute long intervention video immediately prior to vaccination. In the active control condition, participants will view a matched video that is designed to be mood neutral. Pre-and-post positive affect levels will be assessed by self-report questionnaires. Immune response to the intervention and vaccination responses will be assessed in saliva (pre/post intervention) and serum samples (pre/4 weeks post-vaccination/16weeks post-vaccination) respectively.

Inclusion Criteria:

• Males and Females aged 65-85 years (inclusive)
• Received influenza vaccination for the 2016/17 season
• Eligible to receive 2017/18 influenza vaccination as part of usual care
• Ability to give informed consent

Exclusion Criteria:

• Males and Females aged less than 65 or over 85 years (exclusive)
• Did not receive influenza vaccination for the 2016/17 season
• Ineligible to receive 2017/18 influenza vaccination as part of usual care
• Unable to provide informed consent

Deemed by health care provider to be:

• Too physically frail to participate
• Diagnosed with dementia or other cognitive condition which would make participation difficult
• Insufficient command of English language
• Influenza vaccination contraindicated
• Sufficiently impaired of hearing or vision that exposure to the intervention or control video content as intended would be compromised
• Those for whom the collection of blood samples is contraindicated.

During Primary Study Period - Baseline to 16 weeks post-vaccination.

The study did not include a usual care comparator. Blinding potentially compromised by common reactions of participants to the positive mood intervention (e.g., laughter). Demand characteristics. Lack of ethnic diversity within sample