Covid certificate: why are some people excluded (for the time being)?

The covid certificate came into force in Switzerland on Monday, but not everyone has its QR code. In addition to those who choose not to vaccinate or be tested, several categories of people are excluded, starting with those cured of covid early, who were unable to prove their infection by a PCR test. And even serological tests, which prove the presence of antibodies, do not qualify for the FOPH sesame. But why?