Fig. 5: Reemergence due to immunity evasion.
From: Epidemic spreading under mutually independent intra- and inter-host pathogen evolution
a The SARS-CoV-2 disease cycle. Upon exposure (E, yellow) individuals enter a pre-symptomatic phase (PS, purple), from which they later develop mild (IM), severe (IS) or critical (IC) symptoms, determining the duration of their infected phase and their probability to recover (R, green) or decease (D, grey). The probability of all transitions appears along the arrows, and the typical time-line is shown at the bottom of the cycle. 30% of exposed individuals show no detectable symptoms at all (AS). b, c Under small σ we observe a single infection wave, which tapers off as the susceptible population is exhausted. This captures the classic pandemic curve, with a single wave of infection. d, e Increasing σ we now observe a second infection wave, in which a variant with sufficiently high ϕμ (orange nodes) is able to reinfect the recovered (blue) individuals. f The probability P for reemergence (double peaked η(t)) in function of R0 and σ. For SARS-CoV-2, R0 is estimated at 2.6 (black solid line); Supplementary Section 5.3.
