Effects of an online tailored decision aid to promote informed decision making about maternal pertussis vaccination in the Netherlands: A randomized controlled trial

Introduction: In 2019, maternal pertussis vaccination (MPV) during pregnancy was introduced in the Netherlands. New interventions to promote informed decision making (IDM) about vaccinations are highly needed, especially for new vaccinations. Decision aids (DAs) have the potential to support IDM. This study evaluates the effects of an online DA on IDM and MPV uptake.Methods: Pregnant individuals, recruited for the randomized controlled trial (RCT), who gave informed consent (N = 1,236) were randomly assigned to the control (N = 650; no information) or intervention condition (N = 586; DA at 18 weeks pregnancy). MPV uptake and IDM were primary outcomes, decisional certainty and psychological determinants of MPV uptake were secondary outcomes. Measures were taken at 18 weeks of pregnancy (baseline) and at 20 weeks of pregnancy (post-test); intervention use was logged. Data were analysed using intention-to-treat analyses, logistic regression, and linear mixed regression models.Results: Uptake of MPV was high in our sample (92.3 %). No significant effect of the DA condition on MPV uptake was found compared to the control condition. We found that the DA increased IDM (13 = 0.24, p < .004) and one of its components level of knowledge about MPV (13 = 0.31, p < .004). We also found an increase in decisional certainty (13 = 0.24, p < .004), perceived susceptibility (13 = 0.24, p < .004), severity of pertussis (13 = 0.41, p < .004), and positive affect about MPV (13 = 0.15, p < .004). There was a positive association between dose of the intervention and MPV uptake (13 = 0.05, p < .004). Discussion: The DA seemed effective in promoting IDM about and determinants of MPV uptake. No main effect was found on MPV uptake, but MPV uptake was related to the level of exposure to the DA. People with high intentions towards MPV were overrepresented in the sample. However, effects on IDM were consistent among participants with different levels of MPV intention at baseline.