Potential impact of seasonal forcing on a SARS-CoV-2 pandemic

Richard A Neher; Robert Dyrdak; Valentin Druelle; Emma B Hodcroft; Jan Albert

To match the R 0 estimates for the early outbreak with our parameterization of transmissibility in Eq. 2 we need to account for the fact that December/January are winter months in Hubei and peak transmissibility in Hubei likely corresponds to θ ≈ 0 (0 being the beginning of the year, so a θ in December/January). An R 0 ≈ 3 in winter in Hubei and a seasonal forcing of ε = 0.4 implies an annual average R 0 = β 0 /ν = 2.2. This reasoning leads to our parameter choice of β 0 = 158/year, ν = 72/year, θ = 0. We assume the outbreak started at t = 2019.8 in Hubei with one infected individual and use N = 6 × 10 7 as population size. To incorporate infection control measures, transmissibility is reduced by 50% once prevalence reached 3% (third order Hill-function, see Supplemental Material). Introductions to a location like Northern Europe with ε = 0.5 (i.e. slightly stronger seasonal forcing then Hubei) are assumed to happen at a rate of 0.01 per year for each infected individual elsewhere. The simulation of the SIER model in different regions is deterministic, but migration is implemented stochastically by Poisson resampling of the average number of migrating individuals. Fig. 3 shows simulated trajectories of SARS-CoV-2 prevalence in the temperate Northern Hemisphere assuming the outbreak started in Hubei early December 2019. Depending whether the peak transmissibility of SARS-CoV-2 in the northern temperate zone is in November, January, or March, the simulation predicts a main peak in the first half of 2020, a main peak in winter 2020/2021, or two similarly sized peaks.