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 =1L(l03mL)

II.Calculation of Estimated Particles/Dose

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