BackgroundExpanding fiscal space for health can be defined as providing additional budgetary resources for health, which is highly important during biological crises. This study aimed to provide a model for financing the treatment costs during biological crises using the development of the fiscal space approach.MethodsThis study employed a descriptive mixed-method design, consisting of three stages. In the first stage, a systematic review of relevant literature was conducted using multiple databases, including Scopus, PubMed, and Google Scholar. A total of 45 studies that met the inclusion criteria were selected. In the second stage, a panel of 14 experts identified five primary and 32 secondary strategies using an open questionnaire. Any additional strategies not identified during the literature review were added if a consensus was reached by experts. In the final stage, the Best Worst Method (BWM) was used to prioritize the identified strategies and sub-strategies based on their feasibility, effectiveness, quick yield, and fairness.ResultsFive strategies and fifty sub-strategies were identified. The most important strategies were the increase in health sector-specific resources (0.3889), increase in efficiency of health expenditures (0.2778), structural reforms (0.1111), health sector-specific grants and foreign aid (0.1667), and conducive macroeconomic conditions (0.05556). The most important sub-strategies were establishing and increasing earmarked taxes for the health sector (0.0140), expanding Universal Health Coverage (UHC) plans (0.0103), attracting the participation of non-governmental organizations (NGOs) and charitable organizations in the health sector (0.0096), integrating basic social insurance funds (0.0934), and tax exemptions for economic activists in the health sector (0.009303) during the crisis.ConclusionThis study identified five main strategies and 50 sub-strategies for financing the treatment costs during biological crises. The most important strategies were increasing health sector-specific resources, improving efficiency of health expenditures, and implementing structural reforms. To finance health expenditures, harmful and luxury goods taxes can be increased and allocated to the health sector during crises. UHC plans should be improved and expanded, and the capacity of NGOs and charitable organizations should be better utilized during crises.