This study presents a dual‐method approach to systematically analyze public health advisory networks during the COVID‐19 pandemic across four jurisdictions: Belgium, Quebec, Sweden, and Switzerland. Using network analysis inspired by egocentric analysis and a subsystems approach adapted to public health, the research investigates network structures and their openness to new actors and ideas. The findings reveal significant variations in network configurations, with differences in density, centralization, and the role of central actors. The study also uncovers a relation between network openness and its structural attributes, highlighting the impact of network composition on the flow and control of expert advice. These insights into public health advisory networks contribute to understanding the interface between scientific advice and policymaking, emphasizing the importance of network characteristics in shaping the influence of expert advisors. The article underscores the relevance of systematic network descriptions in public policy, offering reflections on expert accountability, information diversity, and the broader implications for democratic governance.