The age distribution of mortality from novel coronavirus disease (COVID-19) suggests no large difference of susceptibility by age

Ryosuke Omori,Ryota Matsuyama,Yukihiko Nakata

doi:10.1038/s41598-020-73777-8

Ryosuke Omori, Ryota Matsuyama + Show 1 more

Open Access

https://doi.org/10.1038/s41598-020-73777-8

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Abstract

Among Italy, Spain, and Japan, the age distributions of COVID-19 mortality show only small variation even though the number of deaths per country shows large variation. To understand the determinant for this situation, we constructed a mathematical model describing the transmission dynamics and natural history of COVID-19 and analyzed the dataset of mortality in Italy, Spain, and Japan. We estimated the parameter which describes the age-dependency of susceptibility by fitting the model to reported data, including the effect of change in contact patterns during the epidemics of COVID-19, and the fraction of symptomatic infections. Our study revealed that if the mortality rate or the fraction of symptomatic infections among all COVID-19 cases does not depend on age, then unrealistically different age-dependencies of susceptibilities against COVID-19 infections between Italy, Japan, and Spain are required to explain the similar age distribution of mortality but different basic reproduction numbers (R0). Variation of susceptibility by age itself cannot explain the robust age distribution in mortality by COVID-19 infections in those three countries, however it does suggest that the age-dependencies of (i) the mortality rate and (ii) the fraction of symptomatic infections among all COVID-19 cases determine the age distribution of mortality by COVID-19.

Highlights

Since its emergence, coronavirus disease 2019 (COVID-19) has resulted in a pandemic and has produced a huge number of cases worldwide[1]
Our result shows variation of susceptibility among age groups measured by the exponent parameter φ can explain the age distribution of mortality by COVID-19 (Fig. 2a)
The age distribution of mortality formed by the age-dependency of susceptibility is influenced by the value of R0 (Fig. 2b), which cannot explain the similarity in age distributions of mortality among Italy, Japan, and Spain

Summary

Introduction

Coronavirus disease 2019 (COVID-19) has resulted in a pandemic and has produced a huge number of cases worldwide[1]. As of May 29, 2020, the number of confirmed cases in Italy was 382.3 (per 100,000 population), with 507.2 in Spain, and 13.2 in Japan[1] Of those infected, it has been reported that elderly individuals account for a large portion of fatal cases inducing a large heterogeneity in the age distribution of mortality[2,3,4]. An increase in severity will result in a higher mortality rate and subsequently a rise in the number of fatal cases This assumption is reasonable because elder age as well as the existence of comorbidities, which are likely with aging, have been reported as risk factors for severe COVID-19 infections[8,9,10,11,12,13]. We estimated and compared the age-dependent susceptibility in Japan, Italy, and Spain to argue the existence of heterogeneity in susceptibility among age groups

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Conclusion