Transmission Dynamics, Heterogeneity and Controllability of SARS-CoV-2: A Rural-Urban Comparison.

Yuying Li,Xiaohua Zhou,Xin Gai,Yunjun Zhang,Taojun Hu

doi:10.3390/ijerph18105221

Abstract

Few studies have examined the transmission dynamics of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in rural areas and clarified rural–urban differences. Moreover, the effectiveness of non-pharmaceutical interventions (NPIs) relative to vaccination in rural areas is uncertain. We addressed this knowledge gap through using an improved statistical stochastic method based on the Galton–Watson branching process, considering both symptomatic and asymptomatic cases. Data included 1136 SARS-2-CoV infections of the rural outbreak in Hebei, China, and 135 infections of the urban outbreak in Tianjin, China. We reconstructed SARS-CoV-2 transmission chains and analyzed the effectiveness of vaccination and NPIs by simulation studies. The transmission of SARS-CoV-2 showed strong heterogeneity in urban and rural areas, with the dispersion parameters k = 0.14 and 0.35, respectively (k < 1 indicating strong heterogeneity). Although age group and contact-type distributions significantly differed between urban and rural areas, the average reproductive number (R) and k did not. Further, simulation results based on pre-control parameters (R = 0.81, k = 0.27) showed that in the vaccination scenario (80% efficacy and 55% coverage), the cumulative secondary infections will be reduced by more than half; however, NPIs are more effective than vaccinating 65% of the population. These findings could inform government policies regarding vaccination and NPIs in rural and urban areas.

Highlights

The dynamics of an outbreak depend on the average reproductive number (R) and individual heterogeneity in transmission
Primary and secondary severe acute respiratory syndrome (SARS)-CoV-2 infections are identified through (i) active screening of incoming passengers in Hebei Province, especially those have travelled to areas defined by the Chinese government [22] as medium- or highrisk to capture travel-associated symptomatic and asymptomatic infections; (ii) passive surveillance in hospitals and outpatient clinics, involving testing of individuals suspected to have COVID-19 in order to capture symptomatic cases; (iii) contact tracing of all confirmed infections identified by the above screening, followed by systematic monitoring of their close contacts, in order to capture symptomatic and asymptomatic infections; and (iv) city-wide nucleic acid tests (NAT) to capture symptomatic and asymptomatic infections
Considering the effectiveness of interventions, we found that the effect of vaccinatbe better than that of the current non-pharmaceutical interventions (NPIs) implemented in rural areas, while current control is ing all personnel would be better than that of the current NPIs implemented in rural areas, superior to vaccinating 65% of the population

Summary

Introduction

The dynamics of an outbreak depend on the average reproductive number (R) and individual heterogeneity in transmission. Diseases with high heterogeneity show infrequent but explosive epidemics; for example, in 2003, many settings experienced no epidemic despite unprotected exposure to severe acute respiratory syndrome (SARS) cases [2,3], whereas a few cities suffered explosive outbreaks of SARS [4,5]. Few studies explore the impact of asymptomatic infection on disease dynamics, especially individual heterogeneity in transmission. This is likely due to the lack of a valid statistical model and ambiguity of fundamental epidemiological questions that remain poorly understood, such as the proportion of asymptomatic cases [6].

Methods

Results

Discussion

Conclusion