Background: During health emergencies, leading healthcare organisations, such as the World Health Organization (WHO), the European Centre for Disease Control and Prevention (ECDC), and the United States Centers for Disease Control and Prevention (CDC), provide guidance for public health response. Previous studies have evaluated clinical practice guidelines (CPGs) produced in response to epidemics or pandemics, yet few have focused on public health guidelines and recommendations. To address this gap, we assessed health systems guidance (HSG) produced by the WHO, the ECDC, and the CDC for the 2009 H1N1 and COVID-19 pandemics. Methods: We extracted HSG for the H1N1 and COVID-19 pandemics from the organisations' dedicated repositories and websites. After screening the retrieved documents for eligibility, five assessors evaluated them using the Appraisal of Guidelines Research & Evaluation - Health Systems (AGREE-HS) tool to assess the completeness and transparency of reporting according to the five AGREE-HS domains: "Topic", "Participants", "Methods", "Recommendations", and "Implementability". Results: Following the screening process, we included 108 HSG in the analysis. We observed statistically significant differences between the H1N1 and COVID-19 pandemics, with HSG issued during COVID-19 receiving higher AGREE-HS scores. The HSG produced by the CDC had significantly lower overall scores and single-domain scores compared to the WHO and ECDC. However, all HSG scored relatively low, under the median of 40 total points (range = 10-70), indicating incomplete reporting. The HSG produced by all three organisations received a median score <4 (range = 1-7) for the "Participants", "Methods", and "Implementability" domains. Conclusions: There is still significant progress to be made in the quality and completeness of reporting in HSG issued during pandemics, especially regarding methodological approaches and the composition of the guidance development team. Due to their significant impact and importance for healthcare systems globally, HSG issued during future healthcare crises should adhere to best reporting practices to increase uptake by stakeholders and ensure public trust in healthcare organisations.