Comparison of Pragmatic and Explanatory Design Characteristics in Influenza Vaccine Trials: A Retrospective Assessment Using PRECIS-2

Randomized controlled trials evaluating the same intervention may generate fundamentally different forms of evidence depending on their design. The Pragmatic-Explanatory Continuum Indicator Summary-2 (PRECIS-2) framework assesses pragmatism across nine trial design domains. We conducted a retrospective methodological comparison of FLUNITY HD, a registry-based pragmatic randomized influenza vaccine trial, and its prior explanatory benchmark trial, FIM12. All PRECIS-2 domains were evaluated using publicly available documentation, with higher scores indicating greater pragmatism. Two investigators independently scored all applicable domains, with discrepancies resolved by consensus. FLUNITY-HD demonstrated consistent pragmatic alignment, with applicable domains scoring 4-5. This was driven by broad eligibility criteria, routine clinical care settings, and registry-based outcome ascertainment to evaluate vaccine effectiveness against hospitalization and severe clinical outcomes. In contrast, FIM12 exhibited highly controlled structures, with domains predominantly scoring 1-2. This explanatory approach included restrictive eligibility criteria, specialized research environments, protocol-mandated surveillance, and laboratory-confirmed endpoints aimed at isolating biological vaccine efficacy under controlled conditions. Comparative application of PRECIS-2 demonstrates that pragmatism is a multidimensional structural property rather than a binary classification. Domain-level assessment clarifies how distinct trial architectures align with different evidentiary priorities and inferential scopes, supporting interpretation and integration of complementary vaccine evidence across regulatory, clinical, and public health decision-making contexts.