Rapid evaluation of risk communication and population acceptance following detections of vaccine-derived poliovirus in wastewater, Germany, 2024–2025

Technical Summary: Rapid Evaluation of Risk Communication and Population Acceptance Following cVDPV2 Detections in Germany (2024–2025)

Problem Statement
Following the detection of circulating vaccine-derived poliovirus type 2 (cVDPV2) in wastewater samples across nine German cities in late 2024, public health authorities faced a complex communication challenge. Although Germany has been polio-free since 1998 and utilizes only the inactivated poliovirus vaccine (IPV), vaccination coverage for a complete series remains suboptimal (77%), leaving over 180,000 children without full protection. The detection of cVDPV2 in multiple locations, with unclear sources and potential for local transmission, necessitated a rapid response. However, the situation was characterized by scientific uncertainty regarding the extent of transmission and the specific risk to the population. Consequently, authorities implemented "limited" risk communication activities aimed primarily at healthcare personnel and parents of children up to 16 years old, focusing on checking vaccination status and closing gaps. There was an urgent need to evaluate the reach and impact of these limited communications and to assess whether specific population segments, particularly those with populist political orientations known for vaccine hesitancy, were effectively reached or remained vulnerable.

Methodology
The study employed a rapid, nationwide cross-sectional online survey conducted in February 2025, two months after the initial risk communication activities and three months after the first wastewater detection.

• Study Population: A random sample of 1,785 parents of children aged 0–16 years was recruited from the "Health in Germany" panel, a newly established infrastructure at the Robert Koch Institute (RKI) for monitoring vaccine demand.
• Sampling Strategy: The sample was stratified by age, gender, and education within federal states, with a target of 1,250 parents (equally split between children aged 0–5 and 6–16). Data were weighted using inverse probability weighting and adjustment weighting to align with population statistics.
• Survey Instrument: The questionnaire assessed:
  1. Reach and Knowledge: Exposure to public health calls to action, recall of specific messages (e.g., "check status," "get catch-up vaccination"), and factual knowledge regarding polio and the wastewater detections.
  2. Compliance: Self-reported checking of vaccination status and recent vaccination behavior (within the last 3 months).
  3. Psychological Determinants: The "5C" model (Confidence, Complacency, Constraints, Calculation, Collective Responsibility) and risk perception (likelihood and severity) were measured using validated scales.
  4. Political and Social Factors: Voting intention (dichotomized into populist vs. non-populist leaning based on party affiliation), institutional trust, and media consumption patterns (specifically "alternative media").
• Statistical Analysis: Analyses were performed in R. Descriptive statistics were applied to weighted data. Multiple logistic regressions assessed associations between psychological determinants and vaccination status. Mediation analyses (using PROCESS for R) were conducted to explore whether institutional trust and alternative media consumption mediated the relationship between populist political orientation and vaccination status.

Key Results

• Communication Reach: Only 28.3% of parents reported receiving a public health call to action. Among those who did, recall of the core messages was moderate (61.1% recalled the need for catch-up vaccination). Crucially, epidemiological knowledge gaps persisted; only 27.5% knew about the wastewater detections, and 8.0% were aware that Germany had been polio-free for decades.
• Compliance and Gaps: Despite the communication efforts, approximately 17% of children remained incompletely vaccinated. While parents who received the message were slightly more likely to have vaccinated their child recently, the primary drivers for recent vaccinations were routine health check-ups rather than the specific risk communication.
• Psychological Drivers: Vaccine acceptance was generally high. Logistic regression identified vaccine confidence (OR = 1.80) and complacency (OR = 0.57, where lower complacency correlates with higher uptake) as the strongest psychological predictors of vaccination status. Perceived severity of the disease was also significantly associated with uptake, whereas perceived likelihood was not. Practical barriers were reported as negligible (85% found it easy to access vaccination).
• Political Orientation and Vulnerability: Approximately 18% of participants supported populist parties. This group was significantly less likely to have received the public health message (21.3% vs. 34.3%) and had lower vaccination coverage.
• Mediation Effects: Mediation analysis revealed that the association between populist political orientation and lower vaccination uptake was partially explained by two factors:
  1. Institutional Trust: Populist leaning was negatively associated with trust in institutions, which in turn positively predicted vaccination.
  2. Alternative Media: Populist leaning was positively associated with the consumption of alternative media, which was negatively associated with vaccination.
     However, even after controlling for these mediators and the 5C psychological factors, a significant direct effect of populist orientation on vaccination status remained, suggesting additional unmeasured mechanisms.

Significance and Claims
The paper claims to provide the first rapid, population-level assessment of risk communication effectiveness following a cVDPV2 detection in a polio-free country with high but incomplete vaccination coverage. The study highlights that while limited risk communication achieved moderate reach and maintained message coherence, it failed to substantially reduce existing vaccination gaps.

The authors emphasize that the detection of cVDPV2 in wastewater serves as a critical early warning system, yet translating this scientific signal into actionable public behavior is challenging when the risk is perceived as low or the communication is overly technical and reassuring. A central contribution of the work is the identification of populist political orientation as a significant vulnerability factor in public health crises. The study demonstrates that this group is harder to reach through traditional channels, holds lower institutional trust, consumes different media, and maintains lower vaccination rates independent of general vaccine confidence.

The authors conclude that while the German population generally exhibits high vaccine confidence and perceives polio as severe—factors that could support a robust response in a future escalation—the current communication strategies are insufficient for reaching politically polarized segments. The paper asserts that future public health strategies must move beyond general messaging to address the specific trust deficits and media ecosystems of these difficult-to-reach populations to prevent vulnerability during health crises.