Virus quantification

Virus quantification is counting or calculating the number of virus particles (virions) in a sample to determine the virus concentration. It is used in both research and development (R&D) in academic and commercial laboratories as well as in production situations where the quantity of virus at various steps is an important variable that must be monitored. For example, the production of virus-based vaccines, recombinant proteins using viral vectors, and viral antigens all require virus quantification to continually monitor and/or modify the process in order to optimize product quality and production yields and to respond to ever changing demands and applications. Other examples of specific instances where viruses need to be quantified include clone screening, multiplicity of infection (MOI) optimization, and adaptation of methods to cell culture.

There are many ways to categorize virus quantification methods. Here, the methods are grouped according to what is being measured and in what biological context. For example, cell-based assays typically measure infectious units (active virus). Other methods may measure the concentration of viral proteins, DNA, RNA, or molecular particles, but not necessarily measure infectivity. Each method has its own advantages and disadvantages, which often determines which method is used for specific applications.^[1]