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5.3.1.3 What is a vaccine titre?

The titre of a vaccine reflects its potency. For modified live virus vaccines, the titre is an expression of the amount of viral particles present. Different systems can be used: some vaccine titres are expressed in Foci Forming Units (FFU) and others are expressed in Tissue Culture Infected Dose 50 % (TCID50) or plaque forming units (PFU). These expression systems are based on the titration method used and cannot be compared directly with each other.

Furthermore, titres of the same product determined by different laboratories can give different results as a result of methodological differences (titration procedures, calculation of titres, materials used, etc.).Therefore, the titre of the product given by the producers, national licensing bodies or external laboratories based on the producers’ SOP used for licensing is the should be considered the most accurate.

All vaccine titres used during studies conducted as part of the licensing/registration procedure by the manufacturer for safety and efficacy studies are based on the same titration method and are therefore comparable.


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Version 1 - Last updated November 2012