WHO carries out periodic reassessment of all prequalified vaccines. The frequency, scope and need for reassessment are based on quality risk management principles, and influenced by considerations including:
- stringency of oversight exercised by the responsible NRA,
- prior experience with the manufacturer and the specific product,
- variations to the product indicated in annual reports since the previous assessment,
- interruptions to production and/or supply to United Nations agencies,
- reported quality complaints and adverse events following immunization (AEFIs)
- any failure to meet the WHO recommendations and/or the specifications of the offer to bid
- results from targeted testing of batches supplied to UN agencies.
A letter to the manufacturer requesting submission of an updated PSF or CTD for reassessment is sent 6 to 12 months prior to the time of the proposed assessment. Unless a paper copy is requested by WHO, the updated PSF/CTD will be in electronic form only. The updated PSF/CTD should contain a change control section, which indicates the sections that have been changed from the previously submitted PSF/CTD.
Only sections indicated as changed will be evaluated as a part of the reassessment. Items indicated in the change control section will be compared with summary tables of variations that have been submitted annually and to the file that was submitted initially.
Testing of samples during reassessment is required only when there is insufficient evidence of continued compliance with specifications of the WHO annual targeted testing programme of batches supplied to UN agencies.
Consideration of the need for, and scope of a site audit at the time of reassessment will consider the demonstrated history of regulatory inspection of the facility by the national regulatory agency (NRA) (including reports of good manufacturing practice inspections by the NRA).
If, as a result of the reassessment, a vaccine is deemed to be no longer compliant with the WHO-recommended standards, it vaccine will be removed from the WHO List of Prequalified Vaccines. Failure of a manufacturer to participate in the reassessment procedure will also lead to removal from the list.