Javier is a Principal Scientist at MHRA South Mimms, where he leads the Polio Laboratory Group. He earned his PhD from the Universidad Autónoma de Madrid, developing a novel method to generate genetically modified synthetic influenza viruses for prospective vaccine design. He then spent four years as a postdoctoral scientist at the National Institute for Medical Research (Mill Hill, London), continuing his work on influenza. In 1998 he moved to the National Institute for Biological Standards and Control (now MHRA), where he heads the WHO Global Specialized Polio Laboratory, supporting the Global Polio Eradication Initiative in disease surveillance as well as vaccine control, standardisation, and development. In recent years, Javier’s group at MHRA has focused on next-generation sequencing for whole-genome characterisation of poliovirus vaccine strains and surveillance isolates, with the dual aims of establishing robust quality-control methods for vaccine release and deepening understanding of the genetic stability of classic and novel live-attenuated vaccines, including pathways of reversion to virulence. His work has also enabled the establishment of direct detection sequencing methods for poliovirus surveillance, shortening the time to virus identification and accelerating public-health response.