PUBLIC HEALTH · ADOPTION
For five years, a national health authority has observed a continuous decline in ROR vaccination coverage. The national average at 24 months fell from 91 % to 84 % ; in around twelve more vulnerable territories, it dropped below 76 %. Two national campaigns were launched over three years, widely recognized, without any measurable movement in intentions.
The question is not how to convince opponents. It is which intervention architecture produces which reaction in which population — and at what point an intervention intended to restore adoption turns diffuse hesitation into lasting conflict.
THE PROBLEM
The same campaign can reassure, inform, make an appointment easier and reactivate existing trust. In some groups, it can also reinforce a sense of pressure, shift the debate from health to institutions, and turn hesitation into a firmly held position.
The usual levers had been deployed without significant effect. Impact studies of the two previous campaigns showed high message recognition and almost no movement in intentions. Kits sent to treating physicians were rarely used in consultations. Territorial catch-up programs reached only a limited share of uncovered children.
The decision-relevant question was therefore not which message was most convincing, but which intervention produced which reaction in which population — including unintended reactions.
WHAT IS THE SAME FOR EVERYONE
WHAT DIFFERS FOR EACH GROUP
HESITATION IS NOT OPPOSITION
In the source case, only 8 % of hesitant parents are convinced opponents. Grouping all situations of declining coverage into a single category makes the decision impossible to assess : these are different positions that do not react to the same interventions.
These positions lie between practical delay and an already established position. This is not a pathway : no one moves through these stages automatically.
What the simulation makes visible is that the same intervention does not encounter the same thing depending on where a person sits along this spectrum.
ADOPTION AND POLARIZATION
WHAT A CAMPAIGN MEASURES
Message recognition. The two previous national campaigns achieved high levels.
WHAT IT DOES NOT MEASURE
Actual movement in intentions. It was almost nil, despite substantial budgets and careful execution.
WHAT REALLY DIFFERENTIATES
Lived healthcare experience, relationship with the healthcare professional, political context of the territory.
WHERE CONFLICT FORMS
Where a firm national message encounters structural distrust of central authorities.
WHAT A NATIONAL AVERAGE TELLS YOU
A level of coverage, and how it changes. It indicates an aggregate result, not how that result is distributed.
WHAT A TERRITORIAL DISTRIBUTION TELLS YOU
The same program can be positive in eight territories and negative in four. Average progress can coexist with localized deterioration.
Adoption and polarization are two distinct dimensions. In this case, the firm national campaign increases coverage in eight territories and lowers it in four : a positive average can mask a negative political dynamic.
WHAT IS TESTED
Three structuring options were on the steering committee's table : firm national campaign, targeted territorial plan, equipping treating physicians. Each was tested on the actual populations of the territories with declining coverage, then developed into variants by kit, messenger and media treatment.
4 800 synthetic parents distributed across the 18 typologies were exposed to the 34 communication formats tested, in randomized order, with an average of eight follow-up questions per person. Coverage trajectories were then projected over 24 months, territory by territory, producing 96 trajectories for the eight finalist scenarios retained by the committee.
SIMULATED POPULATION
The reconstructed population covers 2,4 million parents of children aged 12 to 24 months, distributed proportionally across the twelve territories with declining coverage, calibrated on public data from INSEE, Santé publique France and annual vaccination-coverage surveys. No personally identifiable data entered the system.
It is structured into 18 hesitation typologies built by combining six dimensions : personal healthcare experience, institutional trust, scientific cultural capital, family and social environment, media exposure, and territorial political context.
ESTABLISHED TRUST
vaccination schedule followed without discussion, stable relationship with the treating physician
PRACTICAL DELAY
appointments postponed, schedule delayed, no disagreement in principle expressed
UNRESOLVED QUESTION
a specific question left unanswered, reactivated at the moment of the decision
MODERATE HESITATION
intermediate trust, decision kept open, high sensitivity to the messenger
POOR HEALTHCARE EXPERIENCE
contradictory information, insufficient listening, poorly explained complication
LOW INSTITUTIONAL TRUST
structural distrust of central authorities, often in a territory already polarized
HIGH TRUST IN THE PHYSICIAN
distrust of national institutions coexisting with willingness to listen to the treating physician
STRUCTURED OPPOSITION
around 8 % of hesitant parents: a reasoned position connected to organized networks
These configurations reveal part of the population's heterogeneity. The simulation operates on synthetic individuals, not a handful of persona types.
REACTIONS
WITHDRAWAL IS EXPERIENTIAL BEFORE IT IS IDEOLOGICAL
Only 8 % of hesitant parents are convinced opponents. The remaining 74 % have experienced one or more poor healthcare interactions in the past five years: a missed appointment, insufficient listening, contradictory information, a minor complication poorly explained. These experiences, unrelated directly to vaccination, crystallize at the moment of the decision.
THE SAME CAMPAIGN PRODUCES TWO OPPOSITE EFFECTS
Projected territory by territory, the firm national campaign raises coverage by 2 to 4 points in eight territories, and lowers it by a further 3 to 7 points in four others. These four territories were already politically polarized on other issues: the reminder to comply becomes a trigger for opposition.
THE MESSENGER IS THE ONLY CROSS-CUTTING PARAMETER
Eight messengers were tested across the 18 typologies. Only one receives favorable attention from all of them: the treating physician. Every other messenger is rejected by at least three typologies. A strategy that systematically equips treating physicians achieves +23 points of coverage in 18 months in the targeted territories.
NATIONAL VISIBILITY OF SUCCESS HARMS THE REMAINING TERRITORIES
Giving successful catch-up efforts national media coverage harms performance elsewhere: success is read as proof that the authorities are instrumentalizing public health. Discreet, professional and local communication progresses faster in the territories that were initially most vulnerable.
Two parents can receive exactly the same information and draw opposite conclusions. For one, “ I need to make an appointment ”. For the other, “ they are telling me what to do again ”. The reaction cannot be read from the content alone : it depends on what that content encounters.
THE MESSENGER
Eight possible messengers were tested across the 18 hesitation typologies. The content does not vary : the attention it receives does. This reading applies to this case and these populations ; it is not a general rule.
SOCIAL DIFFUSION
ADOPTION
coverage can increase at the aggregate level
POLARIZATION
while the intensity of rejection increases in specific territories
STRUCTURE OF OPINIONS
diffuse hesitation can turn into an established position
REVERSIBILITY
an established position unwinds much more slowly than it forms
Making this circulation visible does not indicate which health policy to adopt. It indicates where an intervention changes not only behavior, but the very structure of existing positions.
COMPARISON
Comparative reading derived from simulated reactions. No architecture is cost-free. The national campaign is the most visible and the most exposed to reactance. The territorial plan is better adjusted to local causes, but slower and less legible nationally. Facilitating catch-up resolves practical delays and has little effect on already established opposition. The treating-physician approach requires co-design with the profession; without it, actual kit use remains below 30 %.
THE MOST ROBUST
Equipped treating physicians dialogue kits differentiated by typology paid catch-up consultation national media discretion
THE MOST FRAGILE
Firm national campaign neither territorial differentiation nor local relays
PROJECTION, THEN OBSERVATION
The steering committee selected systematic support for treating physicians : dialogue kits differentiated by typology, a specifically paid catch-up consultation, automated reminders, and national media discretion around territorial progress. The €42 million budget was reallocated : a smaller share for general-public communication and a larger share for treating physicians and territorial infrastructure.
The kits were co-designed with representatives of general practice, then tested in three pilot territories for six months before broader rollout. This co-design, not initially planned, had been identified as critical in the simulations : an imposed kit achieves an actual usage rate below 30 %.
TAKEAWAY
It was experiential and practical : postponed appointments, unanswered questions, poor healthcare experiences resurfacing at the moment of the decision. Among hesitant parents, only 8 % held an established oppositional position. The risk was therefore not failing to persuade enough : it was that firm national messaging would politicize a withdrawal that was not yet political.
An adoption policy is not tested on the persuasive power of its message. It is tested on the distribution of positions in the population concerned, on how much attention each messenger receives, and on what each version of the program changes for situations that do not stem from disagreement.
DECISION
POSSIBLE FUTURES
A
SCALE UP
A firm national campaign, uniform across the territory
B
TARGET
A differentiated territorial plan across the twelve departments with declining coverage
C
WORK THROUGH THE EXISTING RELATIONSHIP
Equipped treating physicians, differentiated kits, easier catch-up, media discretion
METHOD
This case adds a capability to the library : observing that an intervention changes not only behavior, but the structure of positions. Before: diffuse hesitation. After a poorly calibrated intervention: more firmly established positions. The synthetic population makes it possible to explore the sequence action → reaction → discussion → polarization or depolarization, not only action → adoption.
This case is based on a simulation carried out for a national health authority. The institution is not named, no personally identifiable data entered the system, and the detailed results remain the property of the commissioning client. The comparisons between architectures published here are qualitative ; the quantitative values cited are those documented by the commissioning client.
The simulation concerns behavioral reactions to different public-intervention architectures. It is neither a clinical study, nor a medical recommendation, nor an individual prediction, nor an assessment of a vaccine's effectiveness or safety.
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