Priorix-Tetra, a multicomponent vaccine against MMRV (Measles, Mumps, Rubella, Varicella), is presented as a lyophilized vaccine and has to be reconstituted with sterile water for injection. In 2024, the manufacturer GSK  was informed by one OMCL that some Priorix-Tetra lyophilized cakes showed a partly yellowish colour before reconstitution and that white particles were observed after reconstitution. These characteristics did not comply with the registered specifications for appearance. An investigation, started at the manufacturer facility, confirmed that the yellowish cake aspect before reconstitution and the presence of endogenous white particulates after reconstitution are normal characteristics of the Priorix-Tetra vaccine product according to GSK internal documentation. They are inherent to the nature of the product and do not impact the quality, potency and safety of the product. As a corrective action, the manufacturer had to align the registered specifications and label information with its internal operational documents. The responsible OMCLs agreed on a joint interim release strategy with the manufacturer until the approval of the variation. PEI and Sciensano did only issue national certificates for Priorix-Tetra vaccine, no EU certificates. Also, WHO certificates released during this period stated that the appearance test is not conform to the current specification described in the regulatory dossier.