Identification of Worst-Case Model Viruses for Selected Viral Clearance Steps.

Viral clearance validation studies evaluate the efficacy of upstream or downstream process steps for clearing (inactivating or removing) potential viral contaminants from biologics process streams. Inactivation steps are designed to render viruses non-infectious, while removal steps achieve actual physical removal of viruses from the process stream. During validation, the efficacy of viral clearance steps is challenged through evaluation of inactivation and removal capacity, both for viruses known to be capable of infecting the manufacturing process (relevant viruses) as well as for worst-case model viruses (i.e., those believed to be most resistant to removal or inactivation). Worst-case viruses are used to challenge the process steps in order to assure that unknown or novel viruses that may be present in the process stream will be adequately cleared. Historically, the parvoviruses have been used as worst-case models for viral clearance studies due to their small size and lack of a lipid envelope. These characteristics are known to challenge removal by viral filtration and inactivation by a variety of physical and chemical means. In the present paper, we examine the literature on removal of viruses by filtration, and inactivation of viruses by heat, ultraviolet light, and gamma radiation. We conclude that for viral filtration, as well as ultraviolet and gamma irradiation, the use of a parvovirus as a worst-case model virus may not adequately assure that all types of viruses will be cleared using these steps. [ABSTRACT FROM AUTHOR]