Urgent warning after errors in MMRV vaccine administration

Errors in the preparation of MMRV vaccine before administration have left some children unprotected against measles, mumps, rubella and chickenpox.

It has emerged that cases have occurred where Priorix-Tetra® was administered without the freeze-dried vaccine powder being mixed with the supplied diluent.

The error means some infants and young children may have received only the diluent — water for injections. Such children need to be identified and given a further dose of properly reconstituted MMRV vaccine.

One reported cause is the layout of the vaccine pack. Vaccinators may fail to see that an internal protective cardboard cover inside the 10-dose carton must be lifted and removed to expose the vials containing the lyophilised vaccine powder. If the vial is missed, the product is not reconstituted as required by the Summary of Product Characteristics.

The issue first emerged in February 2026, but continued errors have prompted a reminder in the latest edition of Vaccine Update. GSK, the manufacturer of Priorix-Tetra, has also issued a Direct Healthcare Professional Communication letter setting out the error and the steps needed to prevent it.

Before administering Priorix-Tetra®, vaccinators must remove all internal cardboard protective covering so both the pre-filled syringes of diluent and the vaccine vials are clearly visible. They are also being asked to alert colleagues to the risk immediately to help prevent further administration errors.

The 10-dose pack of Priorix-Tetra® contains 10 single-dose vials of vaccine powder, and 10 pre-filled syringes of diluent. ProQuad® MMRV vaccine, supplied in single-dose packs, also requires reconstitution.

UKHSA said vaccinators should familiarise themselves with the packaging, preparation and administration recommendations before giving any new vaccine. Information on reconstitution is available in UKHSA healthcare practitioner guidance, at https://www.gov.uk/government/publications/mmrv-programme-information-for-healthcare-practitioners/mmrv-vaccination-information-for-healthcare-professionals and any suspected or confirmed errors should be reported promptly to the local Screening and Immunisation Team.