Abstract
BACKGROUND: Seasonal influenza vaccination of healthcare workers (HCW) is widely recommended to protect staff and patients. A previous systematic review examined interventions to encourage uptake finding that hard mandates, such as loss of employment for non-vaccination, were more effective than soft mandates, such as signing a declination form, or other interventions such as incentives. Despite these overarching patterns the authors of the review concluded that 'substantial heterogeneity' remained requiring further analysis. This paper reanalyses the evidence using Intervention Component Analysis (ICA) and Qualitative Comparative Analysis (QCA) to examine whether the strategies used to implement interventions explain the residual heterogeneity. METHODS: We used ICA to extract implementation features and trialists' reflections on what underpinned the success of the intervention they evaluated. The ICA findings then informed and structured two QCA analyses to systematically examine associations between implementation features and intervention outcomes. Analysis 1 examined hard mandate studies. Analysis 2 examined soft mandates and other interventions. RESULTS: In Analysis 1 ICA revealed the significance of 'leading from the front' rather than 'top-down' implementation of hard mandates. Four key features underpinned this: providing education prior to implementation; two-way engagement so HCW can voice concerns prior to implementation; previous use of other strategies so that institutions 'don't-go-in-cold' with hard-mandates; and support from institutional leadership. QCA revealed that either of two configurations were associated with greater success of hard mandates. The first involves two-way engagement, leadership support and a 'don't-go-in-cold' approach. The second involves leadership support, education and a 'don't-go-in-cold' approach. Reapplying the 'leading from the front' theory in Analysis 2 revealed similar patterns. CONCLUSIONS: Regardless of intervention type a 'leading from the front' approach to implementation will likely enhance intervention success. While the results pertain to flu vaccination among HCWs, the components identified here may be relevant to public health campaigns regarding COVID-19 vaccination.