Purpose. HL7 Message. Understanding HL is a next-generation interoperability standard created by the standards development organization Health Level(HL7®). Health Levelor HL7 refers to a set of international standards for transfer of clinical and administrative data. It is widely deployed and covers the exchange of information in several functional domains. Why was FHIR created? This Guide is intended for use by immunization registries that want to participate in a strictly-defined record exchan