Use of Vaccines with Diluents

November 2010

Technically Speaking
Monthly Column by Deborah Wexler, MD
Deborah Wexler MD
Technically Speaking is a monthly column written by IAC’s Executive Director Deborah Wexler, MD. The column is featured in The Children’s Hospital of Philadelphia Vaccine Education Center’s (VEC’s) monthly e-newsletter for healthcare professionals. Technically Speaking columns cover practical topics in immunization delivery such as needle length, vaccine administration, cold chain, and immunization schedules.
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Use Of Vaccines With Diluents
Published November 2010
Information presented in this article may have changed since the original publication date. For the most current immunization recommendations from the Advisory Committee on Immunization Practices, visit
Most vaccines come ready to administer in vials or prefilled syringes. However, 11 vaccines need to be reconstituted before being administered: ActHib®, Hiberix®, Menveo®, Menomune®, M-M-R II®, Pentacel®, ProQuad®, Rotarix®, TriHIBit®, Varivax®, and Zostavax®.
To reconstitute a vaccine, a lyophilized (freeze-dried) vaccine in one vial must be mixed with a diluent (liquid) in another. Diluents are not just for dissolving vaccines—they are designed to meet an individual vaccine’s specific requirements in terms of volume, sterility, pH, and chemical balance. In addition, certain vaccine diluents include some of the antigens that are components of the vaccines. For example, the diluent for Pentacel includes DTaP and IPV antigens, and Menveo’s diluent contains the MenCYW serogroup antigens. See Vaccines with Diluents: How to Use Them for details.
In most cases, diluents are not interchangeable (except for the sterile water used in Merck’s M-M-R II, ProQuad, Varivax, and Zostavax). If the wrong diluent is used, the vaccination will always need to be repeated. If an inactivated vaccine is reconstituted with the wrong diluent and is administered, the dose is invalid and should be repeated ASAP. If a live vaccine is reconstituted with the wrong diluent and is administered, the dose is invalid and if it can’t be repeated on the same clinic day, it needs to be repeated no earlier than four weeks after the invalid dose. This spacing is due to the effects of generating a partial immune response that could suppress the live replication of subsequent doses, even of the same live vaccine.*
To minimize loss of vaccine potency, healthcare staff should reconstitute a vaccine just before administering it. Some vaccines must be discarded unless they are given immediately or within 30 minutes after they are reconstituted. Each vaccine’s package insert gives detailed instructions for reconstituting the product. It’s important to read the instructions carefully BEFORE reconstituting the vaccine.
The Immunization Action Coalition (IAC) has developed a handout that lists all vaccines that require diluents, the substance(s) in each freeze-dried vaccine, the substance(s) in each diluent, and the time limit before the reconstituted vaccine product must be discarded. Check out “Vaccines with Diluents: How to Use Them” for more information.
* Editor’s Note: Correction issued December 10, 2012


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