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Modeling the second outbreak of COVID-19 with isolation and contact tracing

The authors are supported by the National Natural Science Foundation of China (12171291, 61873154), the Fund Program for the Scientific Activities of Selected Returned Overseas Professionals in Shanxi Province (20200001), the Key Research and Development Project in Shanxi Province (202003D31011/GZ), the Program for the Outstanding Innovative Teams (OIT) of Higher Learning Institutions of Shanxi, the Shanxi Scholarship Council of China (HGKY2019004), and the Scientific and Technological Innovation Programs (STIP) of Higher Education Institutions in Shanxi (2019L0082)

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  • The first case of Corona Virus Disease 2019 (COVID-19) was reported in Wuhan, China in December 2019. Since then, COVID-19 has quickly spread out to all provinces in China and over 150 countries or territories in the world. With the first level response to public health emergencies (FLRPHE) launched over the country, the outbreak of COVID-19 in China is achieving under control in China. We develop a mathematical model based on the epidemiology of COVID-19, incorporating the isolation of healthy people, confirmed cases and contact tracing measures. We calculate the basic reproduction numbers 2.5 in China (excluding Hubei province) and 2.9 in Hubei province with the initial time on January 30 which shows the severe infectivity of COVID-19, and verify that the current isolation method effectively contains the transmission of COVID-19. Under the isolation of healthy people, confirmed cases and contact tracing measures, we find a noteworthy phenomenon that is the second epidemic of COVID-19 and estimate the peak time and value and the cumulative number of cases. Simulations show that the contact tracing measures can efficiently contain the transmission of the second epidemic of COVID-19. With the isolation of all susceptible people or all infectious people or both, there is no second epidemic of COVID-19. Furthermore, resumption of work and study can increase the transmission risk of the second epidemic of COVID-19.

    Mathematics Subject Classification: Primary: 34D23; Secondary: 92D30.

    Citation:

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  • Figure 1.  The flow diagram of COVID-19 in SIHR model

    Figure 2.  The cumulative number of confirmed cases and unfound infectious cases in China (excluding Hubei province) and Hubei province are shown under the current intervention methods. Where $ CumH $ denotes the cumulative number of confirmed cases, $ Cum I $ is the cumulative number of infectious people, $ I_1+I_2 $ is the unfound infectious people and $ H $ represents the confirmed cases. Other parameter values and initial values are defined in Table Table 1

    Figure 3.  The effect of the isolation of healthy people, confirmed cases and contact tracing measures on the transmission of COVID-19 in China (excluding Hubei province). The top figure shows the cumulative number of confirmed cases and confirmed cases under the current intervention methods. The bottom figure shows the cumulative number of confirmed cases and confirmed cases when the current isolation strategy is not carried out. Where $ CumH $ denotes the cumulative number of confirmed cases, $ Cum I $ is the cumulative number of infectious people, $ S_2+I_2 $ is the quarantined susceptible and infectious people, $ I_1+I_2 $ is the unfound infectious people and $ H $ represents the confirmed cases. Other parameter values and initial values are defined in Table 1

    Figure 4.  The predicted cumulative number of confirmed cases and infectious cases of the potential second epidemic of COVID-19 in China (excluding Hubei province) and Hubei province are shown under the current intervention methods. The embedded figures are the thumbnail of Fig. 2. Where $ CumH $ denotes the cumulative number of confirmed cases, $ Cum I $ is the cumulative number of infectious people, $ I_1+I_2 $ is the unfound infectious people and $ H $ represents the confirmed cases. Other parameter values and initial values are defined in Table 1

    Figure 5.  There is no second epidemic in China (excluding Hubei province) when all susceptible people (top) or all infectious people (middle) or all susceptible people and infectious people (bottom) are isolated. Where $ CumH $ denotes the cumulative number of confirmed cases, $ Cum I $ is the cumulative number of infectious people, $ S_2+I_2 $ is the quarantined susceptible and infectious people, $ I_1+I_2 $ is the unfound infectious people and $ H $ represents the confirmed cases. Parameter values and initial values are defined in Table 1

    Figure 6.  Under the current intervention methods, the top figure shows the effect of the average number of contact tracing $ b $ on the second epidemic of COVID-19 when the time of isolation is 14 days, and the bottom figure shows the effect of the time of isolation on the second epidemic of COVID-19 when the average number of contact tracing $ b $ is 12. Here we assumed that 80% of the susceptible people are isolated in China (excluding Hubei province) on January 30. Where $ CumH $ denotes the cumulative number of confirmed cases, $ Cum I $ is the cumulative number of infectious people, $ S_2+I_2 $ is the quarantined susceptible and infectious people, $ I_1+I_2 $ is the unfound infectious people and $ H $ represents the confirmed cases. Parameter values and initial values are defined in Table 1

    Figure 7.  The effect of resumption of work on the second epidemic of COVID-19 in China (excluding Hubei province) is assessed under the isolation strategy. Where $ 0.8N $, $ 0.5N $ and $ 0.38N $ denote that 80%, 50% and 38% of the susceptible people are isolated on January 30, respectively. Where $ CumH $ denotes the cumulative number of confirmed cases, $ Cum I $ is the cumulative number of infectious people, $ S_2+I_2 $ is the quarantined susceptible and infectious people, $ I_1+I_2 $ is the unfound infectious people and $ H $ represents the confirmed cases. Other parameter values and initial values are defined in Table 1

    Figure 8.  Under the isolation strategy, the effect of resumption of study on the second epidemic of COVID-19 in China (excluding Hubei province) is assessed in case of no school, resumption of study on March 30 and April 20. We assume that 38% of the susceptible people is isolated before school. Here, $ CumH $ denotes the cumulative number of confirmed cases, $ Cum I $ is the cumulative number of infectious people, $ S_2+I_2 $ is the quarantined susceptible and infectious people, $ I_1+I_2 $ is the unfound infectious people and $ H $ represents the confirmed cases. Other parameter values and initial values are defined in Table 1

    Table 1.  Related parameters and initial values in China (excluding Hubei province) and Hubei province

    Related parameters and initial values in (China excluding Hubei province)
    Parameter Descriptions Mean value 95% CI Source
    α1 The time of isolation at home for susceptible people 1/14 [3]
    β The transmission rate of COVID-19 0.3567 (0.3291, 0.3815) Estimated
    b The average number of contact tracing 12 (11.5448, 12.5346) Estimated
    γ The hospitalization rate of infectious people 0.1429 (0.1306, 0.1538) Estimated
    δ The discharged rate from hospital 0.0949 Calculated
    μ The transfer rate from susceptible to isolated susceptible people 1.76 × 10−4 (1.66 × 10−4, 1.86 × 10−4) Estimated
    α2 The transfer rate from isolated susceptible to susceptible people 5.05 × 10−6 (4.95 × 10−6, 5.15 × 10−6) Estimated
    Initial Values Descriptions Mean value 95% CI Source
    N Total population of China (excluding Hubei province) 1.3362 × 109 [3]
    S1(0) The number of initial susceptible people 2.6723 × 108 (2.6723 × 108, 2.6723 × 108) Estimated
    S2(0) The number of initial quarantined susceptible people 3762 (3754, 3772) Estimated
    S3(0) The number of initial isolated susceptible people 1.069 × 109 (1.069 × 109, 1.069 × 109) Estimated
    I1(0) The number of initial unfound infectious people 4101 (4091, 4115) Estimated
    I2(0) The number of initial quarantined infectious people 700 (695,706) Estimated
    H(0) The number of initial hospitalized people 3886 Data
    R(0) The number of initial removed people 64 Data
    Related parameters and initial values (in Hubei province)
    Parameter Descriptions Mean value 95% CI Source
    α1 The time of isolation at home for susceptible people 1/14 [3]
    β The transmission rate of COVID-19 0.3999 (0.3845, 0.4045) Estimated
    b The average number of contact tracing 5 (4.968, 5.1203) Estimated
    γ The hospitalization rate of infectious people 0.1379 (0.1289, 0.1490) Estimated
    δ The discharged rate from hospital 1/18 Calculated
    μ The transfer rate from susceptible to isolated susceptible people 9.983 × 10−6 (9.56 × 10−6, 1.02 × 10-5) Estimated
    α2 The transfer rate from isolated susceptible to susceptible people 4.825 × 10-5 (4.7606 × 10-5, 4.9615 × 10-5) Estimated
    Initial Values Descriptions Mean value 95% CI Source
    N Total population of Hubei province 5.917 × 107 [3]
    S1(0) The number of initial susceptible people 1.18 × 107 (1.18 × 107, 1.18 × 107) Estimated
    S2(0) The number of initial quarantined susceptible people 5367 (5352, 5382) Estimated
    S3(0) The number of initial isolated susceptible people 4.7336 × 107 (4.7336 × 107, 4.7336 × 107) Estimated
    I1(0) The number of initial unfound infectious people 12973 (12963, 12985) Estimated
    I2(0) The number of initial quarantined infectious people 2023 (2014, 2029) Estimated
    H(0) The number of initial hospitalized people 5806 Data
    R(0) The number of initial removed people 320 Data
    Notes: 95% CI: 95% highest posterior density interval.
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