A Systematic Review of Communication Interventions for Countering Vaccine Misinformation

"Heightened vaccine hesitancy that has arisen with Covid-19 vaccines has put to the fore the need to address ubiquitous vaccine mis- and disinformation."

There has been an increase in health-related mis- and dis-information in recent years, with vaccines and infectious diseases a major focus. Misinformation intersects with many potential determinants and can undermine vaccine confidence. This systematic review aims to identify and describe communication-based strategies used to prevent and ameliorate the effect of mis- and dis-information on people's attitudes and behaviours surrounding vaccination (objective 1), as well as to examine their effectiveness (objective 2).

The researchers searched CINAHL, Web of Science, Scopus, MEDLINE, Embase, PsycInfo and MedRxiv in March 2021. For trials addressing objective 2, risk of bias was assessed using the Cochrane risk of bias in randomized trials tool (RoB2).

Of 2,000 identified records, 34 eligible studies addressed objective 1, 29 of which also addressed objective 2 (25 randomised controlled trials (RCTs) and 4 before-and-after studies). Study characteristics are summarized in Table 1, with additional detail on sample characteristics in Appendix Table A1. All but two studies were published within the past decade. 23 studies addressed specific vaccines and/or diseases (most commonly measles, mumps and rubella (MMR) and influenza), while nine studies considered vaccines generally and two used fictitious diseases and vaccines.

The intervention formats and mediums are described in detail in Table 3. They encompassed question-and-answer style pamphlets about childhood vaccines, mock news articles, government announcements, debunking messages posted on social media, and complex interactive strategies delivered both in-person and online. Nine intervention approaches were identified; the distribution of intervention strategies and approaches is displayed in Table 2 of the paper. Most focused on content of the intervention or message (debunking/correctional, informational, use of disease images or other "scare tactics", use of humour, message intensity, inclusion of misinformation warnings, and communicating weight of evidence), while two focused on delivery of the intervention or message (timing and source).

With regard to objective 2, no intervention type showed clear and consistent positive or negative results across outcomes. It is clear, however, that some strategies, such as scare tactics (e.g., using a dramatic narrative about an infant almost dying of measles), appear to be ineffective and may increase misinformation endorsement. Communicating with certainty, rather than acknowledging uncertainty around vaccine efficacy or risks, was also found to backfire. Promising approaches include communicating the weight-of-evidence and scientific consensus around vaccines and related myths, using humour, and incorporating warnings about encountering misinformation. The effects of trying to debunk misinformation, informational approaches, and communicating uncertainty may help with some outcomes but have mixed results and should be investigated further.

Some trials found that a certain intervention was effective at improving attitudes or vaccination intent among some sub-populations but not others. This heterogeneity underscores the complexity of vaccination behaviours and the myriad factors that can influence attitudes, hesitancy, and decision-making. It also highlights the need for communication strategies and interventions to be chosen and tailored in audience-specific ways, and it underscore the need for future trials to conduct rigorous sub-group analyses.

The body of evidence generated by this systematic review points to several considerations for its interpretation and for future research:

1. Many of the studies were randomised trials conducted as simulated situations unlikely to reflect how a communication strategy would be implemented in real life; a messaging approach that works when an individual reads an article embedded in an online survey experiment may not have the same effect when translated into a mass media campaign. Only a handful of studies examined actual interventions as they would be realistically delivered, and most of these did not rigorously assess effectiveness.
2. None of the studies directly measured the effect of interventions on actual vaccine uptake, though many surveyed participants about vaccination intention. Future research in this arena should aim to conduct real-world piloting of interventions and measure resulting changes in uptake of vaccines, in addition to indicators such as vaccination intention, knowledge, and belief in misinformation.
3. Research must keep up with the ever-changing media landscape through which misinformation propagates; future studies should consider how to address misinformation spreading on Instagram, WhatsApp, and TikTok, including how modifying search algorithms, ranking different type of evidence and sources of information, and reporting online misinformation may help address disinformation.