How long after reconstitution (mixing) can I use a vaccine?

Q: I have accidentally reconstituted a Chicken Pox & MMR vaccine (mixed the powder & the diluent) for a child who did not need the vaccine. For how long can I store this vaccine after this?
A. Vaccines should be used immediately after reconstitution if possible. The life of each reconstituted vaccine varies from product to product. Consult the product package insert for the most up-to-date information about expiration dates and times following reconstitution. Unused reconstituted vaccines kept beyond these limits should not be administered. The best way to avoid such waste is to reconstitute and draw up vaccines
immediately before administration.

Shelf Lives of Reconstituted Vaccines

Vaccine	Expiration after Reconstitution
Varicella (Chicken Pox)	30 minutes (protect from light)
DTaP/Hib	30 minutes
MMR vaccine	8 hours (protect from light)
ActHIB®  vaccine (Hib)	24 hours

--> Mark each opened multidose vial with the date it was first opened. Mark reconstituted vaccine with the date and time it was reconstituted. Dating these vials is important for two reasons. First, some vaccines expire within a certain time after opening or after reconstitution. This may not correspond to the expiration date printed on the vial by the manufacturer. For example, multidose vials of meningococcal vaccine should be discarded if not used within 35 days after reconstitution, even if the expiration date printed on the vial by the manufacturer has not passed. Second, dating opened or reconstituted vials helps manage vaccine inventory by identifying vials that should be used first.
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On a slightly different note, Multi-dose vials used for mass immunizations are to be best used as per the following WHO policy

Multi dose vials of OPV, DTP, TT, DT, Td, hepatitis B, and liquid formulations of Hib vaccines from which one or more doses of vaccine have been removed during an immunization session may be used in subsequent immunization sessions for up to a maximum of four weeks provided that all of the following conditions are met:

• The expiry date has not passed;
• The vaccines are stored under appropriate cold chain conditions;
• The vaccine vial septum has not been submerged in water;
• Aseptic technique has been used to withdraw all doses;
• The VVM, if attached, has not reached its discard point.

The revised policy does not change recommended procedures for handling vaccines that must be reconstituted, that is, BCG, measles, yellow fever, and some formulations of Hib vaccines. Once they are reconstituted, vials of these vaccines must be discarded at the end of each immunization session or at the end of six hours, whichever comes first.

The rationale for these differing recommendations is as follows. Most freeze-dried (lyophilized vaccines) do not contain preservatives and consequently must not be kept more than the manufacturer's recommended limit and never longer than six hours after they are reconstituted. Liquid injectable vaccines such as DTP, TT, DT and hepatitis B contain preservatives that prevent growth of bacterial contamination. Should contamination take place within the vial, the action of these preservatives prevents any increase in bacterial growth over time and actually decreases the level of contamination.
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