Different thermal stability of four SARS-CoV-2 variants. (A) The relative infectivity of each variant after incubation at 4, 24, or 37 °C for 8 h as evaluated via the focus-forming assay. (B) Nonlinear regression of the relative infectivity of each variant following prolonged incubation (2, 4, 8, 12, and 24 h) at physiological temperatures (37 °C). (C) Average half-life values for each variant at 37 °C. All error bars indicate the standard errors of the mean. Mean values for the half-life were compared using one-way ANOVA in GraphPad Prism 8.0 software. Statistical significance was set at p < 0.05 (****, p < 0.0001).