in my country, Occupational Health falls under two different ministry.
under the ministry of health, it is a subspecialty of public health. you have to become a public health specialist by completing a DrPH program, which is a PhD. unfortunately, most of them in this pathway are researchers with very little working in the industry.
under the ministry of human resource, it is a set of competency credential alongside other form of safety & health licensing. for medical doctors, these includes Occupational Health Doctor (OHD), Medical Review Officer (MRO), Ergonomic Trained Person (ETP), Competent Medical Impairment Assesor (CMIA), Chemical Health Risk Assesor (CHRA). While these groups of people are not "specialist" per say, they are well respected in the industry.