With the increasing number of coronavirus disease 2019 (COVID-19) cases and worldwide vaccination coverage, ‘vaccination passports’ (vaccination certificates) may become a required permit for global travel, thereby supporting economic recovery. On March 7, 2021, Wang Yi, State Councilor and Foreign Minister of China, announced the launch of the Chinese version of an ‘international travel health certificate’ at a press conference of the National People’s Congress and the Chinese Political Consultative Conference. He proposed a feasible ‘Chinese solution’ for promoting the recovery of the global economy and the facilitation of cross-border travel, and hoped that the international travel health certificate and vaccination passport can be mutually authenticated. The Israeli government issued a vaccination certificate or ‘green passport’ to vaccinees via a smartphone application and the government website, which must be presented when entering places with a high risk of infection such as restaurants and cultural facilities. The European Union (EU) plans to introduce an EU vaccination certificate by the summer of 2021 that includes vaccination records and nucleic acid test results. The government of the Republic of Korea is exploring the implementation of a COVID-19 vaccination passport by issuing vaccination passports to Korean citizens and exempting arriving foreigners with vaccination passports from quarantine.
Mutual trust of electronic vaccination certificates is important to promote the implementation of vaccination passports. The World Health Organization (WHO) issued interim guidance for developing a smart vaccination certificate (hereafter referred to as the guidance) in March 2021 (1), and created the concept of digital vaccination certificates (DVCs) or ‘smart vaccination certificates’ (SVCs). The purpose of SVCs is to provide a mechanism for individuals to submit documents proving that they have been vaccinated, and the certificate can be encrypted and verified by the authorities. SVCs are considered superior to paper vaccination certificates that may be defrauded, lost, damaged, or difficult to read due to illegible handwriting. SVCs were designed for COVID-19 vaccines, but the aim is to establish a basic consensus mechanism applicable to other vaccines in the future. Following the guidance, in this work we propose a technical route for the application of blockchain, the underlying technology of Bitcoin, in trusted DVCs.