Generally speaking, the health certificate is valid for one year, and can be reapplied within one year after the expiration of the health certificate, that is, the participating units can replace the new health certificate after arranging the medical examination in a unified way. If the health certificate has expired or is about to expire, you should re-participate in the health examination of the unit and apply for a new health certificate.
However, the validity period of the health certificate may have different requirements for people with different jobs, and the specific period needs to be consulted with relevant institutions.