Determinants of seasonal influenza and COVID-19 vaccine uptake in high-risk individuals in northern Sweden

Seasonal influenza and COVID-19 vaccination in high-risk individuals prevent disease, disability, and death. Nevertheless, many high-income countries continue to experience suboptimal vaccine coverage. We therefore aimed to identify the remaining vaccination barriers in these settings. We recruited patients seeking emergency department care at a hospital in northern Sweden. Using semi-structured interviews and medical records, we collected high-resolution individual-level data, and linked community-level determinants from national registers. Logistic regression was used to calculate odds ratios (OR) and adjusted odds ratios (aOR) for determinants associated with influenza and COVID-19 vaccination. We included 600 patients of whom 450 were eligible for both vaccines. Coverage among eligible individuals was 52.0% for influenza and 54.2% for COVID-19. Co-administration of both vaccines was high (OR 55.33, 95% CI: 30.86-99.22). Individual-level determinants associated with lower vaccine uptake included male biological sex (aOR: 0.57, 95% CI: 0.37-0.88, younger age (aOR: 0.50, 95% CI: 0.41-0.61), smoking (aOR: 0.43, 95% CI: 0.18-1.02), reduced independence (aOR: 0.59, 95% CI: 0.31-1.10), and age-only eligibility (aOR 0.41, 95% CI: 0.19-0.86). In multimorbid individuals, meeting more eligibility criteria showed no significant association with higher uptake (aOR: 1.14, 95% CI: 0.93-1.39). Finally, we noted only limited influence of community-level determinants. In conclusion, vaccine uptake for influenza and COVID-19 was primarily associated with individual-level determinants, whereas community-level showed little impact. Targeted communication, such as risk-stacking to improve risk-awareness, harmonized eligibility criteria, and co-administration, may help overcome remaining vaccination barriers in high-risk individuals.