Figure 2.
New SARS-CoV-2 variants with high transmissibility (Re > 1) often extinguish with low initial cases, but extinction is unlikely after an early super-spreading event. We simulated the introduction of 1 (i), 10 (ii) or 100 (iii) infected cases (columns) with a given variant into a population of 1 million susceptible individuals and allowed for time-varying viral load, stochastic transmission and super-spreading. (a) Heatmaps illustrate the percentage of simulations that resulted in extinction (blue: no extinction, yellow: frequent extinction) across ranges of super-spread parameter (gamma-distributed network dispersion) and variant reproduction number. Super-spread parameter ranges encompass low (ρ = 0.1, a realistic value for influenza) to high super-spread potential (ρ = 40, an upper estimate of SARS-CoV-2 infection). Ranges of effective reproductive number (Re) encompass values from throughout the COVID-19 pandemic, which can be modulated by factors such as circulating variant transmissibility, social distancing, masking and/or proportion immune at a given time. Note the electronic supplementary material, figure S1 shows that Re is not strongly influenced by the super-spreading parameter. (b) Correlation between extinction probability and peak viral load, coloured by super-spread parameter, illustrate viral load kinetics influence transmission dynamics, particularly for lower dispersion and single-case introduction. Here, peak viral load is a determinant of Re.