Background The COVID-19 pandemic has brought into sharp focus the need for effective and appropriate vaccination policies for the healthcare workforce. Systematic review evidence shows that interventions to encourage uptake of seasonal influenza vaccination of healthcare workers (HCW) that involve hard mandates, such as loss of employment for non-vaccination, are more effective than soft mandates, such as signing a declination form, or other interventions such as incentives. Resistance to hard vaccine mandates during the COVID has been evident. Moreover, residual ‘substantial heterogeneity’ was observed in the review evidence on flu vaccine drives, indicating that factors other than the vaccination policy itself may influence uptake. Using novel reviewing techniques – Intervention Component Analysis (ICA) and Qualitative Comparative Analysis (QCA) – we re-examine the evidence to identify whether implementation strategies moderate the success of mandates and other interventions.

Methods ICA was used to extract authors reflections on what underpinned the success of the intervention they evaluated and information on implementation procedures. Two QCA analyses, informed by the ICA findings, were undertaken. Analysis 1 examined hard mandate studies. Analysis 2 examined soft mandates and other interventions. Each analysis systematically compared more and less successful interventions of that type to identify whether the variation in outcomes observed was associated with implementation features.

Results ICA revealed that authors of the most successful interventions of each type recommended a ‘leading from the front’ (LFF) implementation strategy. Four key components underpinned the collaborative, rather top-down, LFF implementation strategy: strong support from institutional leadership; education prior to implementation; two-way engagement with HCW so they can voice concerns prior to implementation; and previous use of other strategies so that institutions ‘don’t-go-in-cold’ with their approach. QCA revealed that the success of both hard mandates and soft or other mandates were enhanced by a LFF implementation strategy. For hard mandates, either of two configurations were associated with greater success. The first involves strong leadership support, two-way engagement, and a ‘don’t-go-in-cold’ approach. The second involves leadership support, education and a ‘don’t-go-in-cold’ approach. Analysis 2, on soft mandates and other interventions, revealed similar patterns.

Discussion A thoughtful approach to the implementation of flu vaccination drives among HCW, characterised by a ‘leading from the front’ approach, will likely enhance intervention success regardless of the basic intervention strategy. Given the current prevalence of vaccine hesitancy, these findings may be relevant to ongoing public health campaigns regarding COVID-19 and other vaccinations.