Covidcheck only checks the validity of your certificate, it does not store your certificate. https://covid19.public.lu/en/covidch...rtificate.html From experience, I know it works on an EUDCC, and also on the UK NHS QR code wtihout conversion. It is not possible to 'convert' your US CDC card into an EUDCC in Luxembourg unless you are a resident. However, there are other countries (eg Switzerland, Germany) which will convert your CDC card and issue you a certificate, which should work in the Covidcheck app (ie give a green tick when it is scanned) but I have not tried this.