SOAPTransport Protocol

Enhancing EHR-IIS Interoperability
The Centers for Disease Control & Prevention (CDC) 

Immunization Information System Support Branch (IISSB)

initiated the Electronic Health Record (EHR)-Immunization 

Information Systems (IIS) Interoperability Enhancement Project to 

provide support for the enhanced interoperability of EHRs with 

IIS, specifically focusing on the exchange of vaccination records. 

The CDC established a panel of subject matter experts (SMEs) 

and reviewers to evaluate and analyze currently utilized industry 

transport protocols and recommend the most suitable option for 

EHR-IIS interoperability. 

The Transport Layer Expert Panel consisted of 41 industry experts 

representing:

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Office of the National Coordinator (ONC)

CDC Public Health Informatics and Technology Program 

 Office (PHITPO)

American Immunization Registry Association (AIRA)

Electronic Health Record Association (EHRA)

Indian Health Service (IHS)

IIS vendors

EHR vendors

IIS programs

The panel conducted a thorough investigation and comparison of five 

transport protocol options:

ebXML (PHINMS)

SMTP+S/MIME (Direct Project)

SFTP

HTTPS POST/REST

SOAP

The panel’s intent was to identify and recommend a unified 

technical interoperability framework for immunization-related 

transport that would allow for both broad adoption and longterm viability as an industry standard.

Panel members identified Simple Object Access Protocol (SOAP) 

as the protocol that can meet the current and future needs of IIS 

data exchange and that also has the best chance for broad 

adoption across disparate healthcare systems. While the panel 

recommended SOAP, it significantly acknowledged the role and 

value of the other transport layer options. It was not the 

expectation of the panel or of the EHR-IIS Interoperability Project 

that IIS programs discontinue the use of existing transport 

protocols or those currently under development. The panel’s 

findings do not represent a mandate for IIS programs but rather 

a recommendation to move toward standardization in the 

immunization community.

Each protocol was 

evaluated against 

20 agreed-upon 

business requirements, 

as well as the 

HL7 2.5.1 

Use Cases. 
Best Chance for Broad Adoption Across Disparate Systems

This is a key factor in the success of any technology decision but is even more important for an 

interoperability project. The panel addressed this by looking at key stakeholders, 

prior implementations, and industry trends

Wide Usage by EHR Community

The 2011 Integrating the Healthcare Enterprise (IHE) Connectathon, the largest interoperability 

testing event for the healthcare IT industry, included 40 EHRs that support SOAP.

Natural Language Syntax

From a developer standpoint, multiple SOAP development and support tools exist, ranging from 

open source to privately-licensed software. There is also a large community of practice, web 

resources, tutorials, and example code to heighten ease of use.

Machine-Readable Contract/WSDL

SOAP has a machine-readable contract between the sender and receiver to describe its conventions, 

such as how and where to specify authentication credentials, that is referred to as a Web Services 

Definition Language (WSDL). This allows for a clear interface across all healthcare systems. The panel 

created its own WSDL to provide a common contract for query/response between EHRs and IIS and 

therefore reduce implementation timelines.

Usage by IIS Community

Several IIS are either live with a SOAP web service or working toward a SOAP service. Currently, these 

include: Arizona, Colorado, Kansas, Massachusetts, Missouri, Nevada, New York City, Oregon, Utah, 

and Wisconsin.

Support for Current and Future HL7 Messages

If immunization messaging moves towards HL7 Version 3 with XML-based messages, SOAP has the 

ability to transport streams of text as well as object models.

Support for Future Interoperability Initiatives

The SOAP transport methodology supports the long-term goals of immunization messaging 

interoperability and future potential Meaningful Use requirements.

Findings

The panel’s findings were formally presented at the National Immunization Conference (NIC) in 

March 2011. The collaborative work of the panel was documented in a 75-page Recommendations 

Document which details the panel’s methodology, the justifications for its recommendation, a 

detailed acknowledgement of the other transport protocols, and a summary of the impacts of a 

SOAP implementation. The Recommendation Document can be found on the IISSB web site at:

http://www.cdc.gov/vaccines/programs/iis/interop‐proj/downloads/ehr‐interop‐trans‐layer‐tech‐recs.pdf

Justification of SOAP Selection
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By identifying SOAP 

as a recommended 

transport, EHR vendors 

will be able to focus on 

one transport protocol 

as a baseline for 

interoperability with 

immunization registries, 

while having a protocol 

that is scalable enough 

for the emerging 

requirements for query 

functionality. 

Impact 

The recommendation of SOAP web services has a number 

of effects on the IIS and EHR communities. IIS that have 

implemented a SOAP service have been able to build their 

capabilities over time. This means it is entirely possible to build a 

simple SOAP service which only processes vaccination updates 

at first. Once stable, the IIS can then focus on expanding its SOAP 

service to handle query/response use cases. EHR vendors and 

their clients at healthcare facilities will need to work with IIS to 

connect the software deployed at hospitals, clinics, and private 

doctors’ offices to the IIS. The Electronic Health Record Association (EHRA) supports the effort to recommend a single transport 

option that member companies would utilize for immunization 

interoperability. When technology companies need to assign 

resources for the same clinical functionality (exporting/importing 

immunization information to/from registries), but with different 

technical implementations, it increases the cost to the entire 

stakeholder base. 

Resources 

To support the SOAP recommendation, the expert panel 

developed SOAP Implementation Resources in addition 

to the Recommendation Document. These resources include: 

Case studies of SOAP implementation efforts 

Lessons learned 

Documentation of SOAP tools 

Coding samples for the WSDL in Java and .Net 

The panel also developed a Formal Specification Document to 

support software interface engineers and technical project 

managers. For SOAP-based HL7 transmissions to an IIS, the 

Specification describes operations, parameters, and faults, as well 

as addressing transport and security. 

All resources and references can be found on the IISSB 

web site at: https://www.cdc.gov/vaccines/programs/iis/technical-guidance/

soap/service

Contact Information 

Stuart Myerburg 

Centers for Disease Control and Prevention 

1600 Clifton Rd 

Atlanta, GA 30333 

404-639-1813

http://www.cdc.gov/ 

SOAP CS234370-A

Reviewed February 2016