Lyophilized (freeze-dried) vaccines are powders or pellets that must be mixed with
a liquid (diluent) in a process known as reconstitution before they can be administered.
Diluents vary in volume and composition. Diluents are NOT interchangeable, unless specified by the manufacturer (e.g., the diluent for MMR, MMRV, VAR, and HZV). Use only the specific diluent provided by the manufacturer for that vaccine to ensure adequate potency and safety of the resulting mixture. If a vaccine must be reconstituted with sterile water or saline, use only what is supplied by the manufacturer for that vaccine. NEVER use stock vials of sterile water or normal saline to reconstitute vaccines. Mark the vaccine vial with the date and time it is reconstituted.
Contact your state or local health department immunization program, the vaccine manufacturer, or CDC for guidance if a vaccine has been reconstituted with the wrong diluent and inadvertently administered. A vaccine reconstituted with the wrong diluent and inadvertently administered should generally be repeated.