This is applicable to those viruses for which an estimate of starting numbers can be made, such as endogenous retroviruses.

Example:

I. Assumptions

Measured or estimated concentration of virus in cell culture harvest = 106/mL

Calculated viral clearance factor = > 1015

Volume of culture harvest needed to make a dose of product = 1 L (l03mL)

II. Calculation of Estimated Particles/Dose

Therefore, less than one particle per million doses would be expected.