Ask ten public health communicators what makes a campaign work, and most will start with the same word: trust. The research increasingly agrees — but it also complicates some comfortable assumptions about what actually builds it.

This piece isn’t built around a single interview. It’s a synthesis of what’s already on the record — published research, public remarks, and government guidance from people who study why public health messages succeed or fail — organized as a conversation with the field itself.

“A Relationship Problem, Not a Misinformation Problem”

Heidi Larson, an anthropologist and founding director of the Vaccine Confidence Project, a World Health Organization Centre of Excellence, has spent two decades studying why people accept or refuse vaccines. Her recurring diagnosis cuts against the instinct to simply correct bad information: “We have a relationship problem, not a misinformation problem.”

Larson’s Vaccine Confidence Index tracks four dimensions of public sentiment: whether people believe vaccines are safe, effective, important, and compatible with their personal or religious beliefs. Her research has found that hesitancy rarely stems from a single false claim — it accumulates from a broader erosion of trust in institutions, which then makes people receptive to information that confirms their doubts, whether or not it’s true. Correcting the specific claim does little if the underlying relationship between the public and the institution delivering the message stays broken.

That view leads Larson toward a counterintuitive kind of transparency. Rather than projecting total certainty, she has argued publicly that health institutions do better acknowledging the limits of what they know: “There are real adverse events. We don’t know the answers to all of the parents’ questions.” Admitting uncertainty, in her research, tends to build more durable trust than insisting on message discipline.

The Appeal — and the Limits — of Social Proof

If trust is one pillar of behavior change, “everyone else is doing it” messaging has long been considered another. Descriptive-norms messaging — telling people that most of their peers already recycle, vaccinate, or get screened — has been a staple of behavioral-science-informed campaigns for over a decade, built on foundational social psychology showing people take behavioral cues from others.

But a systematic review and meta-analysis published in Nature Human Behaviour in September 2025 complicates that consensus considerably. Researchers led by Trisevgeni Papakonstantinou, working with colleagues including Natalie Gold of the London School of Economics, pooled results from 89 randomized controlled trials covering nearly 86,000 participants. Their initial analysis found a small positive effect of social norms messaging on health behavior (Cohen’s d = 0.14). But once the team corrected for publication bias — the tendency for studies with striking results to get published more often than studies with null results — the effect shrank to statistically indistinguishable from zero (d = 0.01).

The authors’ conclusion is blunt: on the corrected evidence, social norms messages “are not effective at improving health behaviours,” and no version of the approach — different message types, delivery channels, or target behaviors — reliably outperformed the rest. It’s a significant reversal of what had been treated as one of behavioral science’s more exportable, low-cost tools, and a reminder that even techniques with a strong theoretical pedigree need re-testing as more rigorous methods become available. The honest read of the current evidence is that social-proof messaging alone is not a dependable lever — not that it never works, but that it hasn’t been shown to work reliably enough to justify treating it as a default strategy.

Meeting Communities Where the Distrust Actually Lives

Where the research converges more clearly is on specificity. In 2023, the U.S. Centers for Disease Control and Prevention published guiding principles for what it calls equity-centered public health communication — practical guidance built from communication-science literature and the agency’s own pandemic-era experience. The principles push practitioners to frame health disparities in their social and structural context, rather than implying that affected communities are responsible for their own outcomes, and to use specific, accurate references to the population being addressed rather than broad, flattening categories.

That emphasis on specificity echoes Larson’s own approach at the Vaccine Confidence Project, which relies on monitoring social media and local sentiment to diagnose what a particular community is actually worried about — a school-specific safety concern, a past harm, a distrust of a particular institution — rather than deploying identical national messaging everywhere and hoping broad reassurance sticks.

Put together, the emerging picture is less a formula than a discipline: information alone rarely moves behavior, borrowed social-psychology shortcuts like norms messaging don’t reliably move it either once tested rigorously, and the campaigns that do work tend to be built on a specific, honest relationship with a specific audience — not a bigger megaphone.

Sources: Heidi Larson, Founding Director, Vaccine Confidence Project, remarks via TEDMED (massivesci.com); Trisevgeni Papakonstantinou, Natalie Gold, et al., “A systematic review and meta-analysis of the effectiveness of social norms messaging approaches for improving health behaviours in developed countries,” Nature Human Behaviour, September 2025 (nature.com); U.S. Centers for Disease Control and Prevention, “CDC’s Guiding Principles to Promote an Equity-Centered Approach to Public Health Communication,” Preventing Chronic Disease, July 2023 (cdc.gov).