Modeling the COVID-19 outbreaks and the effectiveness of the containment measures adopted across countries

Edward De Brouwer; Daniele Raimondi; Yves Moreau

Limitations of the model. The SEIR model does make important assumptions and shows significant limitations. The size of the population is considered constant without births and external deaths. Given the time scale for studying the epidemics here, this assumption is likely to have a negligible effect. Next, individuals who have recovered from the disease are considered to be immune. Based on what is known about SARS-CoV-1 and SARS-CoV-2, which are closely phylogenetically related, it is reasonable to assume that individuals who recover from COVID-19 will benefit from immunity at least over the period modeled here. Also, it has been reported that asymptomatic and mildly symptomatic individuals (who will not be recognized as carrying the disease), and presymptomatic individuals (during at least 2-3 days of the incubation period) are likely to be contagious with a degree of infectivity that is not yet well characterized. The SEIR model does not account for these effects and the high value of β obtained might in part be caused by the need to account for those missing contagion events. Moreover, the number of symptomatic individuals might also be underestimated because testing is in some cases being focused on most severe cases, which similarly will lead to the inflation of β and R 0 . More sophisticated models (with more patient compartments) might better capture the different effects described before, but such models will have significantly more free parameters, which means that those parameters might simply be unidentifiable from the available data or that overfitting is likely.