Currently (since the lifting of the O-N(-T) rules) this type of certificate is not issued. It usually was not accepted abroad.
This type of certificate can be issued only to persons whose practitioner has saved to the ISIN system an information stating that they, due to possible medical issues (mostly an allergy to any of the vaccine components), cannot get vaccinated against COVID-19. It cannot be used itself separately as proof of having met the O-N(-T) requirements - this is the role of the certificate about a negative PCR test result. Should a person's Tečka (Dot) app not contain a certificate about contraindication (visible as yet another certificate) together with a negative PCR test result, the test result will be accepted only to the extent that vaccination is not contraindicated in him/her.