Fig. 11.

Threshold conditions for recurrent outbreaks of the same lineage and the factors influencing them. Subplots (a), (b) represent the effect of the rate of loss of cross-immunity on the outbreak final size of the recurrent outbreak of the same lineage, where ${\eta }_1=6e-4$ is the threshold condition for the recurrent outbreak of the same lineage. The blue filler indicates the range of ${\eta }_1$ values for the current Omicron stage, in which case recurrent outbreaks of Omicron strains will result in the final size. The white filler indicates the possible scenario of recurrent outbreaks in future strains. (c), (d) show the effect of the rate of loss of immunity on the outbreak final size and specific timing of recurrent outbreaks of the same lineage. Non-resurgence represents that the same lineage strain will not resurgence.(For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)