Virus removal/inactivation is a major concern in the safety of monoclonal antibodies (MAbs) and other recombinant-protein drugs. Some methods (such as nanofiltration and low-pH inactivation) have been demonstrated repeatedly by the industry to be reliable for most viruses, with >4 log10 removal. Based on my company’s virus-removal experiences with its MAb downstream-process platform, we propose a “bracketing method” — testing only samples that lie at the extremes of a design space — to prove proactively that small differences in operating…