CBRN Intelligence and Information Sharing Act of 2021 This bill expands the functions of the Office of Intelligence and Analysis of the Department of Homeland Security related to homeland-security focused intelligence and information sharing. The office shall support intelligence analysis and risk assessment of terrorist actors, their claims, and their plans to conduct attacks involving chemical, biological, radiological, and nuclear materials against the United States, including critical infrastructure; support intelligence analysis and risk assessment of global infectious disease, public health, food, agricultural, and veterinary issues; leverage existing and emerging homeland security intelligence capabilities and structures to enhance early detection, prevention, protection, response, and recovery efforts with respect to a chemical, biological, radiological, or nuclear attack; and share information and provide tailored analytical support on these threats to state, local, tribal, and territorial authorities and to relevant national biosecurity and biodefense stakeholders and other federal agencies.