Digital documentation of COVID-19 certificates: vaccination status: technical specifications and implementation guidance, 
27 August 2021
https://www.who.int/publications/i/item/WHO-2019-nCoV-Digital_certificates-vaccination-2021.1


Overview
This is a guidance document for countries and implementing partners on the technical requirements for developing digital information systems for issuing standards-based interoperable digital certificates for COVID-19 vaccination status, and considerations for implementation of such systems,-- for the purposes of continuity of care, and proof of vaccination. --

Creepy doc from the WHO
Could use a DETAILED analysis