OVERVIEW AND ABSTRACT: This is the 'silent' slide deck, including extra Question-and-Answer session slides, from a presentation at The Open University's Knowledge Media Institute on 19th May 2020, in which we describe the workings of the world's first blockchain-based mobile app for certifying and verifying COVID-19 antibody test results and vaccinations. A full video replay of the 20-minute talk, as well as the full 30-minute followup question and answer session, and related academic papers, can be found at https://blockchain.open.ac.uk/#covid-19 ----------[ABSTRACT OF TALK FOLLOWS]---------- As the COVID-19 Pandemic of 2019/2020 unfolds, a controversial 'Immunity Passport' has been mooted as a way to enable individuals to return back to work or be admitted to current off-limits locations. Our approach is less dramatic, concentrating on the soundness of certification and verification: While the quality of antibody testing and the likelihood of even attaining COVID-19 immunity continue to be researched, we address the issues involved in providing certification for antibody testing and likely future vaccination, in a tamper-proof, privacy-preserving, and ethically appropriate manner. To do this, we developed a prototype mobile phone app and requisite decentralised server architecture. Personally identifiable information is only stored at the user's discretion, and the app allows the end-user selectively to present only the specific test result with no other personal information revealed. Behind the scenes it relies upon (a) the 2019 World Wide Web Consortium standard called 'Verifiable Credentials', (b) Tim Berners-Lee's decentralized personal data platform 'Solid', and (c) a consortium Ethereum-based blockchain. Our approach enables both verifiability and privacy in a manner derived from public/private key pairs and digital signatures, generalized to avoid restrictive ownership of sensitive digital keys and/or data. The app and decentralised server architecture offer a prototype proof of concept that is readily scalable, applicable generically, and in effect 'waiting in the wings' for the biological issues, plus key ethical issues discussed in the presentation, to be resolved. Full replay, academic papers, and related material can be found at https://blockchain.open.ac.uk/#covid-19