Randomised Controlled Trial of a Theory-based Intervention to Prompt Front-line Staff to Take up the Seasonal Influenza Vaccine

Social norms are tacit societal rules that guide how people believe they ought to interact with each other. This individually randomised controlled trial (RCT) evaluated the effectiveness of reminder letters informed by social normative theory (a type of "nudge theory") on uptake of seasonal influenza vaccination by front-line hospital staff at a large acute care hospital in England.

The University Hospitals Birmingham NHS Foundation Trust (UHB) approached the National Institute for Health Research (NIHR) Collaboration for Leadership in Applied Health Research and Care (CLAHRC) West Midlands for support in designing and evaluating the new intervention as part of their seasonal influenza vaccination campaign. Front-line staff employed by the hospital (n=7,540) were randomly allocated to one of four reminder types in a factorial design:

1. A standard letter (no norms) - reminded recipients that taking up the vaccination was important for patient and staff health, informed them that the expected national vaccination rate for front-line staff was at least 75%, and directed them to find more information online or to ask their manager.
2. A letter appealing to descriptive norms (perceptions of how one's peers are behaving) - included the contents of the standard letter and also reported the vaccination rates at similar trusts in England and across all hospitals in the United States (US) for the previous year.
3. A letter appealing to injunctive norms (perceptions of which behaviours are typically approved or disapproved) - included the contents of the standard letter, a personalised salutation, and the signature of the UHB's Chief Executive (who was previously the Medical Director) personally directing the staff to take up the vaccination.
4. A letter containing the contents of the standard letter with the additions of both the descriptive norms and injunctive norms letters.

While the registered protocol describes randomising participants across four letter groups, a fifth group was later created: a "no letter" control group. The researchers examine the possible effect of receiving no letter at all, separately from the prespecified factorial design.

The letters were sent on October 4 2018, which coincided with the beginning of the UHB's staff influenza vaccination campaign. Designed to influence staff behaviour, the campaign included:

• "Communication methods", which made staff aware of the UHB's intention that all staff should have the vaccination as a matter of patient and staff safety. Information was presented in regular staff emails/newsletters, face-to-face team briefings (grand round lectures and induction meetings for new staff), social media (Facebook and Twitter), a video, and posters displayed physically around the hospital and digitally as computer screensavers.
• "Opportunity methods", which made the vaccination available: within the clinical areas where staff regularly work, at advertised vaccination clinics, and at pop-up clinics in the hospital's main entrance and other busy staff thoroughfares.

The norms study was designed to evaluate the marginal effect, if any, of adding "social norms methods" to the standard "communication and opportunity methods" used in the hospital.

In short, there was no evidence that the uptake of the seasonal influenza vaccination was affected by reminders using social norms to motivate uptake. The current trial finds no support for the effectiveness of adding a reminder letter to an existing vaccination campaign, as there was no difference in uptake for participants who were sent a letter and participants in the no letter control group. All trial groups demonstrated a similar vaccination uptake of approximately 43%.

While the "nudge theory" methods used here were not effective, the researchers suggest that a future intervention might draw on the success found for telephone-based interventions (texts and apps) in non-health worker populations. Other "nudges" could be considered, such as requiring unvaccinated staff to wear face protection masks when working with patients during the influenza season. This option arguably infringes on personal liberty but might be justified.