HL7v2 is just the schema - the mechanism for sending these messages is normally something called MLLP which is just a simple framing protocol and has no built in security. It is possible to send/receive HL7v2 over other protocols, MLLP is the most common.
Its normal to secure the endpoints via network level security - ipsec etc. HL7v3 transformed into FHIR which is done over HTTPS instead.
Its normal to secure the endpoints via network level security - ipsec etc. HL7v3 transformed into FHIR which is done over HTTPS instead.