Existing standards are regularly revised, updated and improved on the basis of information provided by national immunization programmes and Prequalification Holders. This information includes:

• product field-testing results
• ongoing user feedback on product performance in the operating environment
• Prequalification Holder feedback on root causes of any product challenges as part of the annual review.

WHO issues two types of standards for prequalification of immunization devices:

• Performance specifications: A performance specification describes the specific environment in which the product will operate and the functional requirements that it must fulfill in order to operate successfully in that environment, thereby establishing a standard of adequate performance, quality and safety.
• Verification protocols: Each performance specification is accompanied by one or more verification protocols which specify the testing procedures that must be used to demonstrate product compliance with the performance requirements. Verification protocols define the type of testing procedure that a product must undergo successfully in order to be prequalified.

Robust post-market monitoring (PMM) of prequalified products drives the development and revision of standards. The process of setting and revising standards through collaboration with a range of key stakeholders guarantees that a product's functional and performance characteristics are optimally adapted to the challenging operating environments of low-resource settings.

Standards under development

The types of challenges faced in the environments in which the WHO Expanded Programme on Immunization (EPI) operates evolve over time. New needs also arise as the resources or the requirements of the immunization programme evolve. In addition, technological advances mean that new types of product and device-solutions may be of benefit for national EPI programmes.

New standards ― performance specifications and verification protocols ― are developed in response to these evolving needs and new opportunities.

Standards under revision

Revision, updating and improvement of existing standards is ongoing, based on information provided by national immunization programmes and Prequalfication Holders. This information includes product field-testing results, ongoing user feedback on product performance and manufacturer feedback on root causes of any product failures.