Backward bifurcation, basic reinfection number and robustness of an SEIRE epidemic model with reinfection

Recent evidences show that individuals who recovered from COVID-19 can be reinfected. However, this phenomenon has rarely been studied using mathematical models. In this paper, we propose an SEIRE epidemic model to describe the spread of the epidemic with reinfection. We obtain the important thresholds R-0 (the basic reproduction number) and R-c (a threshold less than one). Our investigations show that when R-0 > 1, the system has an endemic equilibrium, which is globally asymptotically stable. When R-c < R-0 < 1, the epidemic system exhibits bistable dynamics. That is, the system has backward bifurcation and the disease cannot be eradicated. In order to eradicate the disease, we must ensure that the basic reproduction number R0 is less than Rc. The basic reinfection number is obtained to measure the reinfection force, which turns out to be a new tipping point for disease dynamics. We also give definition of robustness, a new concept to measure the difficulty of completely eliminating the disease for a bistable epidemic system. Numerical simulations are carried out to verify the conclusions.

Does urbanization intensify land finance? Evidence from the county-to-district policy in China

Land finance is one of the economic phenomena in the process of urbanization in China. Studying the impact of urbanization on land finance may help us to better formulate urbanization policies, especially for developing countries. We use the microdata of urban land transactions in China from 2005 to 2016 and adopt a differences-in-differences method based on the county-to-district policy to investigate the impact of urbanization on land finance. We find that the urbanization reform has significantly increased the local government's reliance on land finance. We also find that the policy has a larger impact on land finance for undeveloped cities. Land finance provides a critical source of funds for the urbanization led by local governments, but with the further promotion of urbanization, the reliance on land finance by local governments will show a gradual downward trend. The mechanism test finds that urbanization promotes land finance dependence by increasing the transfer revenue and areas of existing construction land and infrastructure construction investment. The study of the impact of China's urbanization on land finance can serve as a reference for other developing countries' urbanization, and can further provide practical guidance for the promotion of China's new-type urbanization.

Diversified Farming Systems: Impacts and Adaptive Responses to the COVID-19 Pandemic in the United States, Norway and China

The COVID-19 pandemic fully exposed the vulnerability of the global agri-food system to shocks and stresses, highlighting the need for transformation and action to make it more resilient and inclusive. This paper offers a unique insight into the global nature of the COVID-19 pandemic by examining impacts and responses in the agri-food sector within three very distinct contexts, namely the United States, Norway, and China. Focusing on small, diversified farms, the study builds on prior research with the same farmers and support organizations from an on-going collaboration. Firstly, we conducted a short review of policy adaptations to understand how governments, the private sector, non-profit organizations, and communities "stepped up" to provide emergency relief, specialized training, and recovery support for farmers, support that was instrumental in preventing more devastating impacts in all three countries. Secondly, drawing from in-depth interviews with farmers (23) and government and non-governmental support organizations (19), we mapped the vulnerability and resiliency of selected farmers to shocks that severely disrupted traditional supply chains during the COVID-19 pandemic. Data were collected on both the negative and positive impacts of the pandemic to farmer inputs, including labor, operations, and markets, how these changed from the initial lockdowns in early 2020 and through 2021, and on farmer adaptive responses to these impacts. In some contexts, innovation and adaptive responses counteracted negative impacts. We saw diversifying markets, catering to consumer safety concerns, switching to direct and e-markets, hiring in more labor or relying on family labor, and switching to high demand crops and products as the most prominent adaptive responses. Farmers who lacked access to information and government programs, in large part because of language, technology and institutional barriers, missed out on pandemic related opportunities and suffered the most. As we enter the post-pandemic new normal it is important to take stock of lessons learned, and to continue to support those initiatives and innovations that were pivotal not only for weathering the storm, but for building a more inclusive and resilient agri-food system in the long-run.