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Fluzone (Regular and High Dose)

This is a quadrivalent flu vaccine

For a more detailed explanation of some of the ingredients, see this article:


Active ingredients:

4 types of inactive influenza (flu) virus:

  • H1N1

  • H3N2

  • Victoria lineage

  • Yamagata lineage

There is a high-dose version of Fluzone for people 65 and older. The ingredients themselves are exactly the same, but there is a higher amount of both the active and inactive ingredients. Differences in the amount of each inactive ingredient are indicated below.

Inactive ingredients:
Amounts are based on a 0.25 mL regular dose and a 0.5 mL high dose

Buffers: A mixture that resists pH changes.

*In the package insert, it says "QS to appropriate volume" for the amount. QS stands for quantity sufficient. Because this is a 0.5mL vaccine, we can assume that the amount is at most 0.25 mL or 0.5 mL depending on the dose.

Preservatives: prevent bacterial growth and contamination

*Thimerosal is only in multi-dose vials of flu vaccines, which means that one vial of vaccine contains multiple doses. As a result, the container would be reused, so it needs a preservative to prevent contamination between the different uses from the same vial.


Relevant Terms

  • pH: a measure of how acidic or basic a solution is. The scale ranges from 0 (very acidic) to 14 (very basic). A pH of 7 is neutral.

  • Quadrivalent: Protects against four different versions of the pathogen (in this case, influenza virus)

  • Surfactant: a substance like a detergent. They are used in vaccines because they are able to disrupt the membrane (outer layer) of a virus and inactivate it. 

Relevant terms


Last updated: Sep. 17, 2023

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