Identification of Preliminary Core Outcome Domains for Communication about Childhood Vaccination: An Online Delphi Survey

"Vaccination communication interventions impact more than just vaccination status and behaviours. Measuring intermediate outcomes related to the communication's purpose is crucial to unpacking these effects and may assist in understanding the differential effects of interventions intended to address hesitancy."

This article shares the results of an online Delphi survey conducted to identify preliminary core outcome domains for measuring the effects of communication about childhood vaccination. The researchers focused on 3 common types of vaccination communication interventions with potential to address vaccine hesitancy, defined by their purposes: communication to (i) inform or educate, (ii) remind or recall, or (iii) enhance community ownership. Communication strategies for childhood vaccination operate at an interpersonal, community, or population level and are delivered in many different ways, including via face-to-face interactions, print, mail/email, phone/SMS (text message), websites, TV and radio, community events, and live performance.

The researchers explain that parents who are vaccine hesitant fall somewhere in the middle of the continuum between total vaccine acceptance and complete refusal. While they may fully vaccinate their children, they may still feel some degree of reluctance or doubt about this decision, making them more susceptible to misinformation or safety scares. Vaccination rates alone, therefore, give an incomplete picture of hesitancy. To identify whether vaccination communication interventions can reduce hesitancy, additional relevant outcomes need consideration. One way to help researchers and evaluators select and measure relevant outcomes is through the development and use of a core outcome set (COS). A COS is a set of outcomes that stakeholders agree should be measured, at a minimum, in evaluations of a condition or intervention.

Using an online Delphi survey, they asked different stakeholders to rate the importance of outcome domains that could be measured for each communication type. They used stratified purposive sampling to recruit participants from 4 stakeholder groups: (i) parents or community members; (ii) healthcare providers (both professional and lay health workers); (iii) researchers; and (iv) representatives of governmental, inter- or non-governmental organisations (NGOs). They aimed to reach as many participants in low- and middle-income country (LMIC) settings as possible to ensure the COS would include global perspectives. In the end, respondents came from 29 countries.

They then organised all identified outcomes into a taxonomy of vaccination communication outcomes. This taxonomy delineated the 8 outcome domains presented in the survey: "knowledge or understanding", "attitudes or beliefs", "decision-making", "vaccination status and behaviours", "health status and well-being", "communication delivery and design", "community participation", and "cost". For each of the 3 communication types (see above), they asked participants to rate how important they felt it was to measure outcomes from each of the 8 outcome domains using a 5-point Likert scale. A rating of 5 meant the domain was considered "critical"; 3 was "important but not critical"; and 1 was "not at all important".

The most important outcome domain for (i) communication to inform or educate was "knowledge or understanding"; for (ii) reminder communication, it was vaccination status or behaviours; and (iii) for community engagement communication, it was "community participation". Stakeholders rated most outcome domains as very important or critical, with minimal variation in their priorities across groups.

The researchers explore the meanings of these findings in the Discussion section. For example, when ratings for all 3 communication types were averaged, the most highly-rated outcome domain was "vaccination status and behaviours", which is logical and confirms current practice, as trials essentially always measure outcomes from this domain. However, considering outcome ratings for different communication types separately allows us to see, for example, that outcomes associated with community participation were rated as important when evaluating communication strategies that aim to enhance community ownership and engage the community in vaccination issues. Social mobilisation strategies are noted as potentially effective tools to address community-wide vaccine hesitancy, but trials rarely measure outcomes such as level of participation in community coalitions, which limits the growth of evidence in this area.

This finding confirms that communication should not be conceptualised or evaluated as a single (or simple) homogeneous intervention. Trialists are advised to specifically consider the aims of the communication and to select outcomes reflecting these aims. "Trials and evaluations should also consider the potentially different values of stakeholders involved in the communication intervention, and how these might be reflected by the outcomes selected for measurement."