https://www.europarl.europa.eu/at-your-service/files/be-heard/eurobarometer/2021/soteu-flash-survey/soteu-2021-report-en.pdf

https://www.medrxiv.org/content/10.1101/2021.10.21.21265355v2

https://www.bruegel.org/2022/01/the-effect-of-covid-certificates-on-vaccine-uptake-public-health-and-the-economy/

https://ec.europa.eu/info/live-work-travel-eu/coronavirus-response/safe-covid-19-vaccines-europeans/eu-digital-covid-certificate_en#recognition-of-covid-certificates-from-third-non-eu-countries

https://wttc.org/News-Article/WTTC-identifies-digital-solutions-for-governments-worldwide-to-significantly-restore-international-mobility

https://www.iata.org/en/pressroom/2021-releases/2021-08-26-01/

https://vaccinetracker.ecdc.europa.eu/public/extensions/COVID-19/vaccine-tracker.html

https://www.ecdc.europa.eu/sites/default/files/documents/RRA-19th%20update-27-jan-2022.pdf

https://ec.europa.eu/health/health-security-and-infectious-diseases/crisis-management/covid-19-diagnostic-tests_en