Reasons for non-uptake of Influenza Vaccination: comparison between high-risk and non-high risk groups in Portugal. In Portugal, the Influenza Vaccine (IV) coverage remains below the coverage goals proposed by the European Union. Understanding motives for IV non-uptake, particularly for high-risk groups, is essential. One of the most used theoretical frameworks to understand vaccination is the Health Belief Model (HBM). This study aims to describe the Portuguese non-uptake and differences between HBM dimensions (susceptibility, severity, benefits, barriers and cues for action) for high-risk and non-high-risk groups. A cross-sectional study was developed using a probabilistic dual-sampling frame telephone household panel of families in Portugal. The survey was conducted between June-September 2021, with data collected by questionnaire applied in mixed mode to one 18+ years element of each household unit (n=1050). Content thematic analysis was conducted in one open question about the reasons for IV non-uptake and included HBM dimensions. Statistical analysis focused on estimating non-adherence to IV and HBM categories’ frequency stratified by target group. Results were weighted by sex, age group, region, and study design. Of the total sample, 671 individuals did not uptake the IV (69.3%, CI95%:64.8-73.5). For the IV recommended population, non-uptake was 49.8% (CI95%:43.6-55.9). The perception of low Susceptibility was more common in individuals who didn’t belong to the target group (74%, CI95%:63.4-82.3 vs. 26%, CI95%:17.7-36.6). The Barriers dimension was more frequently mentioned by the target population (45%, CI95%:32.4-58.2 vs. 55%, CI95%:41.8-67.6), namely due to unavailability of stock. IV non-uptake was lower for high-risk group, compared to the general population. Differences between the reasons for non-uptake, suggest that the group to whom the IV is recommended, due to increased risk of complications, is aware of increased susceptibility. The vaccination campaign seems to be successfully targeting the high-risk group, even though efforts need to be maintain to decrease non-uptake.