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.