Final answer:
The least interoperability between health information system applications at present is found between Electronic Health Records (EHRs) and Health Information Exchanges (HIEs).
Step-by-step explanation:
In the present time, the two health information system applications that have the least interoperability are Electronic Health Records (EHRs) and Health Information Exchanges (HIEs).
An Electronic Health Record is a digital version of a patient's medical history, which is stored and accessed within a healthcare organization. However, different EHR systems often have varying data formats and standards, making it difficult to exchange information smoothly with other systems.
On the other hand, Health Information Exchanges are platforms that facilitate the sharing of patient data among healthcare organizations. While they aim to promote interoperability, the lack of standardized data formats and inconsistent implementation across entities lead to limited information exchange between EHRs and HIEs.