In December 2019, China reported the first COVID cases to the World Health Organization (WHO). China imposed lockdowns as early as January 2020, Saudi Arabia announced national curfews after only a few hundred cases, with the threat of fines and jailtime. And by mid-March, the UK went into its first lockdown. But how did COVID-19 go on to impact different political regimes - did it support authoritarianism and did it erode democracy? This book discusses what elements of political legitimacy world leaders drew on to justify COVID restrictions. It traces the history of how China, Saudi Arabia, Britain and the United States responded to previous pandemics and to what extent leaders in power attempted to centralize their authority in the years leading up to COVID. As vaccines emerged for COVID, how did Trump's isolationism influence a turn to what became known as vaccine nationalism, while Xi Jinping countered such vaccine hoarding with the belief that COVID vaccines should be a public good? Through analysis of public discourse given in response to COVID and in response to vaccine development, this book uses novel methodology to measure political legitimacy and political persuasion to reveal how COVID affected democratic and non-democratic legitimacy and fed into isolationism and globalization.