https://www.gov.uk/government/publications/university-of-oxford-and-nuffield-college-the-impact-of-mandatory-covid-19-certificates-on-vaccine-uptake-synthetic-control-modelling-of-6-countrie
University of Oxford and Nuffield College: The impact of mandatory COVID-19 certificates on vaccine...
Paper prepared by Univeristy of Oxford and Nuffield College on COVID-19 certificates.
university of oxford
https://www.computerweekly.com/news/252495910/Denmark-and-Sweden-to-issue-digital-vaccine-certificates
Denmark and Sweden to issue digital vaccine certificates | Computer Weekly
Sweden and Denmark announce plans to develop digital certificates that prove people have been vaccinated against Covid-19
and swedendenmarkissuedigitalvaccine
https://www.aa.com.tr/en/europe/turkey-hungary-recognize-each-others-covid-19-vaccine-certificates/2235705
Turkey, Hungary recognize each other's COVID-19 vaccine certificates
May 10, 2021 - Turkey, Serbia also planning to recognize each other's COVID-19 vaccine certificates | Anadolu
covid 19 vaccineeach otherturkeyhungaryrecognize