Vaccine confidence mediates the association between a pro-social pay-it-forward intervention and improved influenza vaccine uptake in China: A mediation analysis

A Chinese clinical trial has demonstrated that a prosocial pay-it-forward intervention that offered subsidized vaccination and postcard messages effectively increased influenza vaccine uptake and vaccine confidence. This secondary analysis explored the potential mediating role of vaccine confidence on the association between a pay-it-forward intervention and influenza vaccine uptake, and how this might vary by individual annual income levels.Data from 300 participants (150 standard-of-care and 150 pay-it-forward participants) were included in the analysis. We conducted descriptive analysis of demographic and vaccine confidence variables. Multivariable regression and mediation analysis on interventions, vaccine confidence and vaccine uptake were conducted. A sub-group analysis was conducted to further understand whether associations between these variables vary by income levels (<=$1860 or >$1860).The pay-it-forward intervention was significantly associated with greater levels of perceived influenza vaccine importance (adjusted odds ratio (aOR) = 3.60, 95 %CI: 1.77-7.32), effectiveness (aOR = 3.37, 95 %CI: 1.75-6.52) and safety (aOR = 2.20, 95 %CI: 1.17-4.15). Greater perceived influenza vaccine importance was associated with increased vaccine uptake (aOR = 8.51, 95 %CI: 3.04-23.86). The indirect effect of the pay-it-forward intervention on vaccination was significant through improved perceived influenza vaccine importance (indirect effect1 = 0.07, 95 %CI: 0.02-0.11). This study further revealed that, irrespective of the individual income level, the pay-it-forward intervention was associated with increased vaccine uptake when compared to the standard-of-care approach.Pay-it-forward intervention may be a promising strategy to improve influenza vaccine uptake. Perceived confidence in vaccine importance appears to be a potential mediator of the association between pay-it-forward and vaccine uptake.