Cold-chain transmission, asymptomatic infection, mass screening, vaccine, and modelling: what we know so far for coronavirus disease 2019 control and experience in China

Coronavirus disease 2019 (COVID-19) pandemic has continued to spread rapidly across the world. In the past nearly two years, there have been over 267million confirmed COVID-19 cases including over five million deaths globally reported toWHO [1]. Facing this unprecedented public health crisis which we have not seen in a century, global experts rapidly expand scientific knowledge on this new virus, to track the spreadandvirulenceof the virus. Different countries develop response strategies and practices tailored to their own specific epidemiological situations, resources, and values of individuals living in their countries [2]. Although first reported, quick containment of COVID-19 was achieved in China. It set an inspiring example for the world. China experienced two stages for COVID-19 response [3]. The first stage began from the first case reported in Wuhan at the end of 2019, and continued until Wuhan ended lockdown on Apr 8, 2020. From then on, the main challenges in the second stage changed from the interruption of widespread community transmission to the prevention of sporadic outbreak resurgence from cases overseas. China’s practice of breaking community transmission, followed by prevention of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) reintroduction from imported cases overseas show that established public health measures will remain the best tool [4]. That is, COVID-19 can be controlled and even eliminated with non-pharmaceutical interventions (NPI) alone (e.g., early detection, early reporting, early isolation, masks, social distancing, and handwashing). Prof Hao and his colleagues from Sun Yat-Sen University will introduce a meta-analysis on the reproductive number of COVID-19, which reflects the COVID-19 transmission dynamic. According to the scale of reproductive number reduction, they conclude that comprehensive interventions and lockdowns were most effective in the pandemic control. In the second stage of COVID-19 response, several sporadic COVID-19 re-emergence outbreaks in China were linked to cold-chain foods or its packaging. Apart from airborne transmission, indirect contact transmission might become a route of infection, by which SARS-CoV-2 was easily transmitted from overseas. Prof Li from Huazhong University of Science and Technology will review the coldchain related COVID-19 epidemics in China, analyze their potential mechanisms and introduce China’s experience in interruption of cold-chain transmission. Asymptomatic and pre-symptomatic infection is a main feature inwhich SARS-CoV-2 isdifferent fromSARS-CoVand Middle East respiratory syndrome coronavirus (MERS-CoV). Compared to these two viruses, the proportion of asymptomatic and pre-symptomatic infections in all cases infected seems higher for COVID-19. Considering their infectiousness and “hidden” distribution in the population, the roles of infections without symptoms should be estimated in this pandemic [5]. We will review the population size, infectiousness, as well as China’s strategy and measures in asymptomatic and pre-symptomatic cases finding and management. With the surge of new SARS-CoV-2 variants, the character of asymptomatic and pre-symptomatic infections may have changed [6]. We also provide related evidence on the changing trend. Mass screening is an important strategy for asymptomatic and pre-symptomatic case finding. However, it is controversial due to its huge social and economic costs, although it has been increasingly used to test close contacts, high risk employees, even all population to ascertain individuals infected. Prof Wang and his colleagues from Beijing Center for Disease Prevention and Control (CDC) *Corresponding author: Liming Li, Department of Epidemiology & Biostatistics, School of Public Health, Peking University, 38 Xueyuan Road, Haidian District, Beijing 100191, China; and Peking University Centre for Public Health and Epidemic Preparedness & Response, Beijing 100191, China, E-mail: lmlee@bjmu.edu.cn Wenjing Gao, Department of Epidemiology & Biostatistics, School of Public Health, Peking University, Beijing, China Med. Rev. 2022; 2(1): 1–2