Examining the Impact of Six Pro-Vaccination Messages on MMR Vaccine Hesitancy Among Mothers in Ukraine: A Randomised Controlled Trial

"The findings illustrate the importance of careful testing when framing government health communications and provide an important example of how behaviourally informed messaging can help in the roll-out of current and future vaccines."

In Ukraine, only 41% of children under 6 are vaccinated against measles, mumps, and rubella (MMR) (Ministry of Health of Ukraine, 2020), and the latest measles epidemic occurred in the 2017-2019 period. The Wellcome Global Survey (2019) attributes the high levels of hesitancy and low levels of vaccine uptake to Ukrainian people holding one of the lowest levels of trust in vaccination globally. One response on the part of the Ukrainian government was to begin delivering mandatory MMR vaccination letters to parents across the country in 2019. This two-phase online randomised controlled trial (RCT) tested 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).

This paper is based on the increasing vaccination model (IVM). The model is founded on the theory of planned behaviour (TPB) and explains behaviour in terms of (i) attitudes, (ii) subjective norms, and (iii) perceived behavioural control. In the case of vaccine hesitancy, a person's attitudes towards vaccines, their understanding of what is normative and appropriate within their social network / the society they live in, and their ease of access to vaccines will all play a significant role in determining their decision to get vaccinated or not. The IVM (Brewer, 2021) extends TPB theory and explains vaccination outcomes in terms of what people think and feel, social processes (including social norms and networks), and opportunities for behaviour change. The focus on thinking and feeling includes risk appraisal (loss- and gain-framed messaging), vaccine confidence, and motivation.

The currently employed Ukrainian mandatory vaccination message could be seen as an example of a loss-framed message due to the loss of access to school for the child of the parent contacted. Gain-framed messages, in contrast, outline the benefits of following a given course of action, such as avoiding infection for oneself and one's family.

In addition to the two common messages - mandatory control and the loss-framed message - this study aimed to select different formulations of messages that would leverage social processes or norms and that would attend to opportunity as potential mechanisms for changing vaccination behaviour:

• The study opted to test two letters containing pro-vaccination social norm statements (one signed by a family doctor and one by a school director). Messages signed by trusted authorities (and explicitly referencing the relevant expertise of the person's authority) could be effective because some groups in society are more trusted than others. Doctors are one particularly promising group here because they are consistently rated as some of the most trusted and respected members of society worldwide and particularly in a Ukrainian context, as trust in other forms of institutional authority is low.
• A doctor testimonial letter, signed by a family doctor, included the doctor stressing that it was their personal and professional recommendation that children should be vaccinated.
• The study also included a letter, signed by a school director, that underlined the lack of barriers to getting one's child vaccinated (focus: the simplicity and accessibility of vaccination procedures). The idea here is that a barrier-reduction message could be effective in Ukraine due to public perceptions of vaccine shortages, common reporting of unavailability of vaccines in emergency departments, and logistical obstacles to vaccine distribution.
• Another letter, signed by a school director, contained a loss-framed message underlining the risks of non-vaccination.

The RCT compared 6 different messages, including a control letter that was a copy of the original mandatory vaccination letter currently distributed in Ukraine, and the 5 other letters described above, which differed in terms of the behaviourally informed content in the letter.

Participants provided consent to take part in a 2-part study about child vaccination, in which they would be asked their opinions and be shown a vaccination-related letter. In phase 1, participants answered a series of questions about vaccination attitudes and intentions, as well as present and prior vaccination behaviour; they also provided sociodemographic information. In phase 2, which followed 2 weeks after phase 1, all participants received one of six virtual letters in their email. After viewing the letter, participants were presented with the option to book a vaccination, followed by a request to answer the same attitude and intention questions from phase 1.

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. Specifically, the social norm - family doctor message had the highest percentage of participants who clicked to schedule a vaccination (75.9%), which was significantly more than the proportion who received the mandatory vaccination (57.7%), barrier-reduction (58.7%), loss-framed (52.5%), and doctor testimonial (61.1%) letters. Further, 64.7% of participants in the social norm - school director condition also clicked to vaccinate, the second highest percentage clicking to schedule a vaccination and a significantly higher proportion than the loss-framed condition.

In short, this research shows that the content and framing of vaccination letters can have an effect on vaccination scheduling behaviour. It also serves as an example of how interventions may affect behaviour independently of attitude and intention. Based on the findings, the researchers conclude that the national template used by Ukrainian public health authorities is unlikely to reduce vaccine hesitancy or increase vaccination rates. Loss-framed messages are likely not effective in a Ukrainian context. "It may be that increasing the social acceptability of vaccinations before such [mandatory vaccination] policies come into effect, at least in (countries similar to) Ukraine, could be important..." Emphasising the normative nature of vaccination could increase uptake in the Ukrainian context.