Examining the Impact of Six Pro-Vaccination Messages on MMR Vaccine Hesitancy Among Mothers in Ukraine

The Ukrainian government began delivering mandatory MMR vaccination letters to parents across the country in 2019. In this two-phase online RCT, we aimed to test the effectiveness of this national mandatory vaccination letter against five behavioural science-informed letters, in terms of their effects on the vaccination attitudes, intentions and behaviours of Ukrainian mothers (N = 738). One letter was focused on the simplicity and accessibility of vaccination procedures; one contained a testimonial from a family doctor; two letters contained pro-vaccination social norm statements (one signed by a family doctor and one by a school director); and one contained a loss-framed message underlining the risks of non-vaccination. The results showed no difference between the conditions in terms of change in vaccination attitudes and intentions but there was an effect on behaviour (measured through clicking a link to schedule a vaccination). The letters signed by a family doctor, outlining how vaccination is a social norm, were most effective in encouraging positive vaccination behaviours. We conclude that the national template used by Ukrainian public health authorities is unlikely to reduce vaccine hesitancy or increase vaccination rates, and that letters emphasising the normative nature of vaccination could increase uptake in the Ukrainian context.