All five COVID-19 outbreaks during epidemic period of 2020/2021 in China were instigated by asymptomatic or pre-symptomatic individuals

INTRODUCTION: The significance of asymptomatic or pre-asymptomatic individuals in driving the COVID-19 epidemic in China or other countries remains uncertain. METHOD: We collected and analyzed all the epidemiologic and virological diagnostic details of the infected individuals released by public health authorities and reiterated every episode of outbreak on a timeline. All individuals associated with the five outbreaks had tested positive for SARS-CoV-2 infection. RESULTS: In this study, all five COVID-19 outbreaks reported in China since October 2020 were analyzed. The Kashgar outbreak in Xinjiang province came into light for the first time on October 22, 2020. However, it was initiated before October 11, 2020, by a local asymptomatic import and export worker, who was infected at the working place. Subsequently, his wife caught the infection, which led to 430 more infections reported in the outbreak. The Beijing outbreak with 41 cases was noticed for the first time on December 22, 2020. However, our analysis revealed that it was initiated by an asymptomatic individual from Indonesia on December 10, 2020. The Shenyang outbreak, with 38 cases, noticed for the first time on December 23, 2020, was initiated by a pre-symptomatic individual from South Korea on December 13, 2020. CONCLUSION: The asymptomatic or pre-symptomatic individuals during the asymptomatic period were unsuspectingly infected by SARS-CoV-2, and unintentionally transmitted the virus to a large number of people. These findings suggest that early detection of asymptomatic or pre-symptomatic individuals is of critical importance in preventing future outbreaks or epidemics.