To reach seasonal vaccination against influenza targets, University Hospitals Birmingham (UHB) already invites staff to take up the vaccination, and every November reminds staff that have not yet vaccinated to do so. The current protocol describes a randomized controlled trial (RCT) in which staff will be sent different reminders, and the investigators will compare the proportion of staff that go on to vaccinate after receiving each reminder.

Seasonal vaccination against influenza is recommended for NHS staff. , To increase vaccination rates, NHS England put forth a Commissioning for Quality and Innovation goal for the 2018/2019 season of 75%. University Hospitals Birmingham NHS Foundation Trust (UHB) wants its vaccination rate to surpass this target. Since staff get infected outside of the hospital and from patients staff vaccination does not provide significant 'herd immunity'

To reach past targets, every September UHB already invites staff to take up the vaccination, and regularly reminds staff that have not yet vaccinated to do so. The current protocol describes a randomized controlled trial (RCT) in which staff will be sent a different letter when first invited to receive vaccination, and we will compare the proportion of staff that go on to vaccinate after receiving each type of letter..

To conduct the RCT the research team will design four letter styles. One factor will emphasize an authority figure inviting staff to vaccinate (the Chief Executive, who is also a doctor). The other factor will emphasize a competitive social norm describing vaccination rates in peer hospitals, including Addenbrooke's, Cambridge University Hospitals (which has exemplary rates) see appendix A and across American hospitals (which also have high rates). Letters will be sent to staff in the first week in October by UHB's communications team and they will be disseminated in a randomized fashion.

The UoW's role in this study is to advise the study's design and write-up the project for publication. UHB will approve the reminders, send the reminders, retrieve the data, and analyse the data. No individual-level data will be transferred across organizations. All individual-level data will be managed by authorized UHB employees, e.g., a UHB statistician will randomize staff to receive different reminders and analyze the data, and UHB's communication team to disseminate the reminders.

Inclusion Criteria:

• All UHB staff eligible for the seasonal influenza vaccination are eligible for this study. (no patients are included)

Individual data will not be shared.

Participants receive one of four types of communications inviting them to take up the influenza vaccination in a randomized fashion. Participants will not be explicitly told that alternative versions of the communications are being sent.