A Very Flat Peak: Why Standard SEIR Models Miss the Plateau of COVID-19 Infections and How it Can be Corrected

Abstract

When actively taking measures to control an epidemic, an important indicator of success is crossing the 'peak' of daily new infections. The peak is a positive sign which marks the end of the exponential phase of infection spread and a transition into a phase that is a manageable. Most countries or provinces with similar but independent growth trajectories had taken drastic measures for containing the COVID-19 pandemic and are eagerly waiting to cross the peak. However, the data after many weeks of strict measures suggests that most provinces instead enter a phase where the infections are in a linear growth. While the transition out of an exponential phase is relieving, the roughly constant number of daily new infections differ widely, range from around 50 in Singapore to around 2000 just in Lombardy (Italy), and 7600 in Spain. The daily new infection rate of a region seems to depend heavily on the time point in the exponential evolution when the restrictive measures were adopted, rather than on the population of the region. It is not easy to point the critical source of these persistent infections. We attempt to interpret this data using a simple model of newer infections mediated by asymptomatic patients, which underscores the importance of actively identifying any potential leakages in the quarantine. Given the novelty of the virus, it is hard to predict too far into the future and one needs to be observant to see if a plan B is needed as a second round of interventions. So far, the peak achieved by most countries with the first round of intervention is extremely flat.

Prediction of Covid-19 Infections Through December 2020 for 10 US States Incorporating Outdoor Temperature and School Re-Opening Effects-September Update

“…On average, a populace maintains an IP value of 2.72, resulting in the unexpected linear infection growth path rather than a more commonly expected "exponential growth" path. Other authors have also noted the unusual linear growth path and used other modeling techniques to simulate this behavior (10,11,12).…”

Spread of COVID-19: Investigation of universal features in real data

“…These plots are shown on a semi-log scale. It is clearly appreciable that n and its rate of change vary drastically from country to country [26]. Even though bending is visible, for some early period the spread may be exponential.…”

Prediction of Covid-19 Infections Through December 2020 for 10 US States Incorporating Outdoor Temperature and School Re-Opening Effects-August Update

“…Linear growth of SARS-CoV-2 infections is observed in many countries. Other investigators (6,7,8) have noticed linear infection growth and noted that traditional disease transmission models do not naturally display linear infection growth trends.…”