Effects of message order and active participation on vaccine risk communication

"Message order" and "active participation" could be effective as risk communication methods. "Anticipated regret" (AR) has also been recognized as affecting risk perception and vaccine uptake in vaccination risk communication. We aimed to evaluate the effects of message order and active participation and the interactions between these two interventions on AR for vaccination.

We conducted a 2 (message order: positive-negative or negative-positive) × 2 (message calendar: with or without planning) factorial design study among 81 study participants. The effects of message order and active participation of mothers, using a message calendar, were evaluated on mothers' decision-making regarding vaccination with Haemophilus influenzae type b vaccine and pneumococcal conjugate vaccine for their children. Participants completed questionnaires to evaluate the AR of infection if unvaccinated (anticipated regret of inaction) and of side effects if vaccinated (anticipated regret of action, ARA) twice: immediately after interventions and 1 month later.

An interaction between message order and active participation was significant with regard to anticipated regret of inaction immediately after interventions (P = 0.01), but this effect disappeared 1 month after interventions. The message order showed no main effect with regard to ARA. However, the main effect of active participation was marginally significant with regard to ARA 1 month after intervention (P = 0.09); AR over vaccine side effects was lower when vaccination was planned than in the condition without planning.

The effect of message order was hardly detectable in a clinical setting. However, active participation induced by planning may affect AR. Further studies are needed to evaluate the effect of active participation in decision-making for vaccination.