Global Health Security and Diplomacy Act of 2020 This bill establishes measures to detect, deter, and contain infectious disease outbreaks overseas before they become global pandemics. The President must establish a Global Health Security Strategy for advancing U.S. global health security and diplomacy objectives. To promote such strategy, the bill establishes the role of Coordinator of U.S. Government Activities to Advance Global Health Security and Diplomacy overseas, who shall coordinate, manage, and oversee U.S. diplomatic efforts and foreign assistance resources. In responding to an international infectious disease outbreak, the Department of State and the U.S. Agency for International Development shall lead diplomatic, coordination, and response efforts. Further, specified foreign assistance funds may be used for the cost to detail or employ certain individuals to carry out programs in response to global health emergencies and natural or man-made disasters. The United States may participate in the Coalition for Epidemic Preparedness Innovations, which is a global partnership focused on developing vaccines to stop future epidemics. The State Department must seek to establish a Trust Fund for Global Health Security within the World Bank. The fund shall enable developing countries to strengthen and sustain health systems and supply chains with the resources, capacity, and personnel necessary to prevent, detect, mitigate, and respond to infectious disease threats before they become pandemics. The Government Accountability Office must report on the effectiveness of the programs, projects, and activities supported by the fund and assess the merits of continued U.S. participation in the fund.