Thea Sesardic has over 35 years’ experience in biomedical research with 25 years’ experience at NIBSC on regulatory research focusing on the 3Rs - replacement, reduction and refinement of animals in the field of biological products derived from bacterial toxins. Over 10 methods have been developed and implemented as part of the batch release function of the group for toxins, antitoxins and toxoid vaccines at NIBSC, reducing the use of animals by 1,000 a year at NIBSC alone. Several of the methods have also gone through international validation and are now regulatory standards. In her capacity as UK delegate on the European Pharmacopoeia group of experts, she has introduced new monographs and method chapters (eg. potency of human tetanus IgG, safety and potency of DT vaccines, replacing toxin challenge methods and replacing LD50 assays for Botulinum toxin for therapy) that continue to impact animal use in Europe and globally. She has contributed to several major revisions and manuals of methods to assess quality, safety and efficacy of DT vaccines as part of a WHO working group.