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Abstract:
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The potency of a biological product of live virus can be determined using either a direct plaque assay or an indirect assay such as 50% tissue culture infectivity dose (TCID50). The former estimates number of infecting particles, while the latter measures the reciprocal of the dilution of virus resulting in infection of 50% of host cells. In this paper, the theoretical relationship between the plaque and TCID50 assays was investigated, through mathematical derivations. The method assumes that the number of infecting particles in a test sample follows a Poisson distribution, and that each unit of the plaque assay titer corresponds to one infecting particle. Under these assumptions, it is shown 1) for the same test sample, the two assays give rise to different titer values; 2) on log10 scale, the difference in titer varies between 0.23 and 0.27 with an average difference being approxima
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