Characteristics and containment of the outbreak caused by the SARS-CoV-2 Omicron variants in Shanghai, China: a retrospective study

ABSTRACT

Objective: The study aimed to describe the characteristics and containment of the Omicron variants in Shanghai compared with the previous severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants in China. Methods: We summarized the data retrieved from the Shanghai Municipal Health Commission from January to June 2022 and the National Health Commission of the People's Republic of China from March 2020 to August 2021. Epidemiological analysis was utilized to describe the differences among SARS-CoV-2 variants and the infection situation in the outbreaks in China. Results: The Omicron variants had the characteristics of high insidiousness, rapid transmission, high infectivity, and short incubation period, which were consistent with the characteristics of outbreaks caused by Omicron in other regions in China and abroad. There were 568978 asymptomatic infections in Shanghai from Feburary 26 to June 30, 2022, accounting for 90.73% of the SARS-CoV-2 infections in this outbreak wave. It's significantly different from a total of 23277 SARS-CoV-2 infections in China between March 31, 2020 and August 8, 2021, of which 41.97% of the cases were asymptomatic infections. Conclusions: Compared with previous outbreaks emerged in China, the Omicron outbreak in Shanghai was characterized by multiple point dissemination, wide coverage, a large number of close contacts of confirmed infections and asymptomatic carriers, and difficult source tracing. The lessons from Shanghai's response to Omicron showed that the dynamic zero-COVID policy is still the most suitable response to the virus which can quickly find the infections and curb the transmission route.