Countries should aim to lower the reproduction number R close to 1.0 for the short-term mitigation of COVID-19 outbreaks

Michael E. Hochberg

Our previous work suggested that population size was an important parameter in how an outbreak unfolds and the impact of mitigation measures (14) . We found that larger populations benefit more in terms of percentage reduced fatalities than do smaller populations. This can be explained in part because the same initial number (10000) of infectious individuals was used in all simulations, meaning that smaller countries were effectively further along in their outbreaks than were more populous ones. Nonetheless, this result and the findings of our previous study indicate that -all else being equal -larger populations have more time to reduce morbidity and mortality in outbreaks than do smaller ones. This insight could apply either to the homogenous populations assumed here, or to spatially subdivided ones, where we would expect delays in outbreaks between different localities. Further investigation is needed to establish how country size may correlate with other potentially important epidemic parameters such as population density and the age and spatial structure of contact networks.