All prequalified immunization products must comply with applicable international standards and WHO-defined performance specifications.

WHO IMD-PQS standards have been developed over many years and in response to the evolving needs of national immunization programmes. Standards are developed in collaboration with national immunization programmes and in consultation with product manufacturers, testing laboratories and a range of technical specialist organizations. Prequalification standards and protocols are regularly revised and updated based on:

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

This process of setting, revising and enforcing 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 medium- and low-resource settings.

How WHO sets and maintains performance standards for immunization devices

WHO prequalification of immunization devices is governed by standard operating procedures (SOPs) that take into account key external standards and processes:

• performance specifications and product verification procedures are informed by international standards
• WHO laboratory accreditation requires laboratories to be ISO/IEC 17025-accredited
• product field-testing procedures are guided by industry-standard protocols.

Performance specifications and verification protocols

Performance specifications and verification protocols are at the heart of WHO prequalification of immunization devices and its standard-setting function. WHO IMD-PQS standards are minimum requirements; they are not restrictive. Applicants seeking prequalified status must be able to verify that their products fulfil the requirements defined in the relevant WHO IMD-PQS product specifications. However, going beyond these requirements with additional features, functionalities or other attributes that improve the product's performance, quality and safety as per user needs is acceptable and encouraged.

Performance specifications

A performance specification describes the specific environment in which the product will operate and defines the functional requirements that it must fulfill in order to operate successfully in that environment. Thus the performance specification establishes standards of adequate performance. The specification refers to applicable published international standards. Specifications also fully comply with WHO immunization policies and guidelines current at the time of publication.

One of the guiding principles of WHO prequalification is to ensure that Prequalification Holders have a fair basis for tender across product categories, countries and geographic regions. Accordingly, performance specifications are comprehensive and unambiguous.

Applicants (manufacturers or licenced resellers) can:

1. Offer compliant products or devices from an existing product range.
2. Modify an existing product or develop a new one.

If no suitable products exist or are forthcoming from manufacturers to meet end users' particular needs, WHO will pursue option two by encouraging selected manufacturers to engage in this development route.

Verification protocols

WHO works to ensure that the requirements defined in product specifications are met via robust verification protocols before prequalified status is granted to a product. Each performance specification is accompanied by one or more verification protocols which specify the testing procedures that must be used to demonstrate that the product complies with the specification.  

Products may be required to undergo one of three types of testing procedure (type-examination, independent type-testing, full quality assurance, see Evaluation for prequalification) according to the volumes that would be deployed and whether or not the product is safety-critical. This ensures that not only are testing procedures time and cost-efficient, but also that the necessary performance, quality and safety standards are met for each product and in the context in which it will be used. The type of testing required for a product is defined in the relevant verification protocol(s).

Field testing

In some specific cases, testing of a product or device in its intended operating environment may also be required to demonstrate that a product meets all prequalification requirements. Field testing is required, for example, for products that include technology not previously used in health programmes in low-resource settings, or that require the creation of a new category of products. WHO is responsible for identifying product types for which field-testing is either mandatory or desirable, and will specify the appropriate generic testing method for each product type.

Field testing demonstrates whether products comply with functional and performance requirements in the intended operating environment. It also provides applicants (product manufacturers) with information to further improve product design and can help end users to choose products that are best suited to their needs. Field testing is carried out by the applicant with the support of testing laboratories and in accordance with protocols established by WHO. Also essential is the active cooperation of the national programme managers of the Expanded Programme for Immunization, and the assistance of technical staff in WHO/UNICEF country and regional offices.

The complete field testing guidance is available here.

The value of WHO standard-setting and norms

WHO leadership in setting standards and norms means that procurement agents and product end-users can be assured of the optimal performance, function and safety characteristics of WHO-prequalified immunization products. Adherence to product standards helps ensure that vaccines stay potent and safe for longer, helps eliminate vaccine wastage and reduces the number of missed opportunities to vaccinate. Ultimately, robust standards for immunization products means that life-saving vaccines reach more health outposts and more children and adults who need them. The prequalification process also provide end-users with the opportunity to provide feedback on product performance. Industry and Prequalification Holders benefit from this feedback and the standards revisions that it helps to inform.