Clinical and public health economic impact of rapid strain-matched vaccination in influenza pandemic mitigation: A UK-like population dynamic transmission model.

Influenza A virus H5N1 has recently circulated at unprecedented levels in birds and mammals, causing sporadic human infections. Using a susceptible-exposed-infectious-recovered (SEIR) dynamic transmission model of a UK-like population, this study aimed to quantify reductions in morbidity, mortality, and healthcare utilization attributable to rapid deployment of a strain-matched pandemic influenza vaccine; to compare outcomes across egg-based and cell-based vaccine platforms; to evaluate the economic impact of nonpharmaceutical interventions (NPIs) and their interaction with vaccination timing; and to estimate the impact of earlier or delayed vaccine availability across a full spectrum of pandemic transmissibility and severity scenarios. In the absence of NPIs, a 16-week vaccination campaign starting 16 weeks post-pandemic declaration reduced infections by 3.0 million and deaths by 28,000, with greater benefits observed in low-transmissibility scenarios. A cell-based vaccine with equivalent timing further reduced deaths by 5.0%, with additional gains in scenarios involving faster vaccine production. NPIs (average cost, £208 billion) enhanced vaccine effectiveness across all pandemic types, most markedly in high-transmissibility events; cell-based vaccine additionally reduced NPI costs by 0.9% relative to egg-based vaccine. Conversely, delays in vaccine availability increased both mortality and economic costs. These findings highlight the need for robust and agile vaccine development, registration, and distribution infrastructures, as well as flexible response strategies adaptable to varying pandemic severity and transmissibility. Policymakers should consider adopting a comprehensive framework integrating health outcome metrics and the economic impact of NPIs to inform vaccine procurement and deployment decisions.