Dr Seth Berkley is an epidemiologist and global health leader whose career has been shaped by one central problem: vaccines save lives, but only if people can actually get them. His 40-year career has spanned the global, from helping to build Uganda’s first HIV surveillance system and founding the International AIDS Vaccine Initiative; to leading Gavi, the Vaccine Alliance for more than a decade – overseeing the immunisation of hundreds of millions of children worldwide. And when COVID-19 struck, Seth co-founded COVAX, the global initiative designed to stop wealthy nations monopolising vaccines. In conversation with Professor Jim Al-Khalili, Seth discusses the highs and lows of his globe-trotting career - from saving millions of young lives through vaccine distribution, to setting his own shattered leg after a climbing accident in Namibia - and addresses the huge challenge of tackling vaccine scepticism.