Randomised controlled trial of a theory-based intervention to prompt front-line staff to take up the seasonal influenza vaccine.

Objective: To evaluate 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.

Design: Individually randomised controlled trial.

Setting: A large acute care hospital in England.

Participants: Front-line staff employed by the hospital (n=7540) were randomly allocated to one of four reminder types in a factorial design.

Interventions: The standard letter included only general information directing the staff to take up the vaccine. A second letter highlighted a type of social norm based on peer comparisons. A third letter highlighted a type of social norm based on an appeal to authority. A fourth letter included a combination of the social norms.

Main Outcome Measure: The proportion of hospital staff vaccinated on-site.

Results: Vaccine coverage was 43% (812/1885) in the standard letter group, 43% (818/1885) in the descriptive norms group, 43% (814/1885) in the injunctive norms group and 43% (812/1885) in the combination group. There were no statistically significant effects of either norm or the interaction. The OR for the descriptive norms factor is 1.01 (0.89-1.15) in the absence of the injunctive norms factor and 1.00 (0.88-1.13) in its presence. The OR for the injunctive norms factor is 1.00 (0.88-1.14) in the absence of the descriptive norms factor and 0.99 (0.87-1.12) in its presence.

Conclusions: We find no evidence that the uptake of the seasonal influenza vaccination is affected by reminders using social norms to motivate uptake.