The plaque assay is a long-standing and standard technique in virology [27, 28] and plaque sizes have been used in many in vitro studies to qualitatively evaluate the phenotypes of various viruses [22, 29, 30] . Plaque assays are often used for strain comparison and, in that context, plaque diameters at a single time point are reported. These plaque diameters are then typically used to conclude that, for example, if the plaques observed at 48 h for strain A are larger than those for strain B, then strain A must have a higher replicative fitness than strain B. However, one should question whether such conclusions are valid and robust to experimental variability. Looking at Figure 2 , one can see that at 36 h, the plaque radius of both A/Brisbane/59/2007 WT and its H275Y mutant counterpart are comparable in size. Yet at 60 h, the WT strain has significantly larger plaques than the H275Y mutant, and the situation is reversed at 96 h. Thus, relying on single time point measurements for comparing strains can be misleading.