Eleven COVID-19 Outbreaks with Local Transmissions Caused by the Imported SARS-CoV-2 Delta VOC — China, July–August, 2021

Abstract

Starting from December 2019, Wuhan, China, encountered the first outbreak of coronavirus disease 2019 (COVID-19) (1-2). The epidemic was successfully suppressed by strict containment so that the number of infected people was reduced to 0 on April 8, 2020 (3-4). After that, China experienced roughly 3 dozen outbreaks with local transmission caused by imported severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). These outbreaks were then contained by an effective suppression strategy, and the number of infected people has successfully reached zero again. However, local outbreaks of COVID-19 have reappeared in several areas in China recently and were caused by the SARS-CoV-2 Delta variant of concern (VOC) (5). As of August 26, 2021, a total of 1,390 cases of COVID-19 have been reported in 50 cities in 19 provincial-level administrative divisions (PLADs) (Figure 1), all of which were found to involve the Delta variant. Furthermore, these cases were found to stem from 12 genetically distinct Delta variant imported sources that were grouped into 11 related outbreaks or sporadic case incidents, resulting in 10 geographically separated epidemics including the following areas (Figure 1): Nanjing City of Jiangsu Province;Zhengzhou City of Henan Province;Xiamen City of Fujian Province;Wuxi City of Jiangsu Province;Dehong City of Yunnan Province;Pudong District of Shanghai Municipality;Songjiang District of Shanghai Municipality;Haikou City of Hainan Province;Ningbo City of Zhejiang Province;and Bortala Prefecture of Xinjiang Uygur Autonomous Region. Starting from July 20, 2021, the number of daily reported infections increased gradually but reached a peak reporting period from July 31 to August 11, 2021. During this peak period, the number of everyday reported cases exceeded 50, and a total of 969 cases were reported during this period, which comprised 69.7% of all cases reported during this series of epidemics. After August 12, the number of daily reported cases decreased significantly.