WHO guidance note: Vaccine diluents, revision 2015

Overview

A vaccine diluent is the liquid mixed with a lyophilized (freeze-dried) vaccine in order to reconstitute the lyophilized vaccine and provide the final vaccine for administration. A vaccine diluent may be sensitive to heat or freezing, and may require transportation and storage in the cold chain. This guidance note outlines the proper handling and use of vaccine diluent, including, but not limited to, critical steps for reconstituting vaccines safely.

Diluent handling
Diluents vary widely in composition, and therefore only the diluent assigned by the manufacturer for the specific vaccine and presentation should be used.* Never replace a vaccine diluent with water for injection, and never inject an oral vaccine or a diluent used to reconstitute an oral vaccine.

Diluent storage
- Unless otherwise specified by the manufacturer, the correct temperature for long-term storage of diluents is +2°C to +8°C.
- Diluent packaged with or attached to the vaccine should always be stored with the corresponding vaccine at +2°C to +8°C.
- Diluent not packaged with the vaccine can be stored at room temperature ONLY if the manufacturer’s instructions allow it. In this case, the manufacturer’s instructions regarding cooling prior to reconstitution should be followed.
- Diluents should NEVER be frozen.
• Wherever possible, vaccines and diluents should be stored in a refrigerator that is reserved for this purpose.
• The vaccine vial monitor (VVM) that is attached to the vaccine vial can serve as a visual trigger to assist a health worker in properly applying the multi-dose vial policy, especially in knowing when the reconstituted product must be discarded.
• All diluents should be managed according to standard storage and warehousing practices for vaccines.

Diluent use 
• The reconstituted product should be discarded at the end of the immunization session, or within six hours of opening, whichever comes first, UNLESS the reconstituted vaccine meets the criteria for keeping the vaccine for up to 28 days, as indicated in the WHO Policy Statement: Multi-dose Vial Policy (WHO/IVB/14.07).
• Vaccinators should be adequately trained to ensure that the diluent used to reconstitute a vaccine is the correct one assigned by the manufacturer.
- Appropriate job aids, such as posters, should be provided.
- Training on the proper handling of diluents should be combined with training on handling multi-dose vials after opening, as specified in the revised WHO Multi-dose Vial Policy