A five-compartment model of age-specific transmissibility of SARS-CoV-2

Abstract

Background: The novel coronavirus, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2, also called 2019-nCoV) causes different morbidity risks to individuals in different age groups. This study attempts to quantify the age-specific transmissibility using a mathematical model.

Methods: An epidemiological model with five compartments (susceptible-exposed-symptomatic-asymptomatic-recovered/removed [SEIAR]) was developed based on observed transmission features. Coronavirus disease 2019 (COVID-19) cases were divided into four age groups: group 1, those ≤ 14 years old; group 2, those 15 to 44 years old; group 3, those 45 to 64 years old; and group 4, those ≥ 65 years old. The model was initially based on cases (including imported cases and secondary cases) collected in Hunan Province from January 5 to February 19, 2020. Another dataset, from Jilin Province, was used to test the model.

Results: The age-specific SEIAR model fitted the data well in each age group (P < 0.001). In Hunan Province, the highest transmissibility was from age group 4 to 3 (median: β₄₃ = 7.71 × 10^{- 9}; SAR₄₃ = 3.86 × 10^{- 8}), followed by group 3 to 4 (median: β₃₄ = 3.07 × 10^{- 9}; SAR₃₄ = 1.53 × 10^{- 8}), group 2 to 2 (median: β₂₂ = 1.24 × 10^{- 9}; SAR₂₂ = 6.21 × 10^{- 9}), and group 3 to 1 (median: β₃₁ = 4.10 × 10^{- 10}; SAR₃₁ = 2.08 × 10^{- 9}). The lowest transmissibility was from age group 3 to 3 (median: β₃₃ = 1.64 × 10^{- 19}; SAR₃₃ = 8.19 × 10^{- 19}), followed by group 4 to 4 (median: β₄₄ = 3.66 × 10^{- 17}; SAR₄₄ = 1.83 × 10^{- 16}), group 3 to 2 (median: β₃₂ = 1.21 × 10^{- 16}; SAR₃₂ = 6.06 × 10^{- 16}), and group 1 to 4 (median: β₁₄ = 7.20 × 10^{- 14}; SAR₁₄ = 3.60 × 10^{- 13}). In Jilin Province, the highest transmissibility occurred from age group 4 to 4 (median: β₄₃ = 4.27 × 10^{- 8}; SAR₄₃ = 2.13 × 10^{- 7}), followed by group 3 to 4 (median: β₃₄ = 1.81 × 10^{- 8}; SAR₃₄ = 9.03 × 10^{- 8}).

Conclusions: SARS-CoV-2 exhibits high transmissibility between middle-aged (45 to 64 years old) and elderly (≥ 65 years old) people. Children (≤ 14 years old) have very low susceptibility to COVID-19. This study will improve our understanding of the transmission feature of SARS-CoV-2 in different age groups and suggest the most prevention measures should be applied to middle-aged and elderly people.

Keywords: Age-specific dynamics; COVID-19; Compartmental model; SARS-CoV-2; Transmissibility.