Presentation (CTI)

OBJECTIVES: Timely and comprehensive monitoring of immunization coverage rates (ICR) is essential following changes in immunization recommendations. Traditional surveillance systems often face delays and incomplete capture of relevant populations. This study evaluates the methodological value of survey-based primary data collection to complement routine surveillance in estimating ICR and understanding immunization behavior across different respiratory disease contexts and seasons.
METHODS: A repeated cross-sectional, survey-based approach was applied following changes in immunization recommendation for seasonal influenza and respiratory syncytial virus in Germany. Standardized online questionnaires captured immunization status, intention, and reasons for and against immunization, alongside socio-demographic and risk-related characteristics. Sampling strategies included stratification and calibration weighting to approximate national population structures. Survey waves were conducted during immunization periods to enable near real-time insights. The approach was designed to complement routine surveillance by capturing immunization uptake in populations that are partially captured or not represented in administrative data sources.
RESULTS: Survey-based primary data enabled timely, in-season estimation of immunization uptake and provided additional behavioural and contextual insights not captured in routine systems. In addition, the approach allowed estimation of ICR in population groups that are typically underrepresented or excluded in official data sources (e.g. members of private health insurances), contributing to a more comprehensive understanding of overall coverage. It further facilitated identification of drivers and barriers to immunization, detection of potential discrepancies with official estimates, and assessment of subgroup variation. Methodological challenges included potential selection bias, recall bias, and limitations related to self-reported data. Weighting procedures mitigated, but did not fully eliminate, these limitations.
CONCLUSIONS: Survey-based monitoring represents a valuable complementary approach to traditional surveillance following changes in immunization recommendations. By enabling faster evidence generation and improving coverage of underrepresented populations, it supports more comprehensive and responsive public health decision-making. Careful interpretation remains essential given inherent methodological limitations.