At what stage should virus inactivation be carried out?

On an industrial scale blood products are produced from plasma pools consisting of donations from thousands of donors. As a number of pathogens may be present in the donor before symptoms of an infectious disease become evident, such pathogens, particularly viruses, may be transmitted in human blood products. The level of virus contamination can be substantially reduced by a range of serological tests and by polymerase chain reaction screening. Viruses can also be removed and/or inactivated during the course of the plasma fractionation process. However, specific virus inactivation steps must be included in the manufacturing process for most blood products. The stage at which these steps should be introduced and the efficacy and drawbacks of various procedures are described.