In a recent study published on the medRxiv * prepress server, researchers evaluated the epidemiological features of the outbreak of the Omicron variant of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in Shanghai, China.
Study: Epidemiological characteristics and transmission dynamics of the outbreak caused by the Omicron SARS-CoV-2 variant in Shanghai, China: a descriptive study. Image credit: Graeme Kennedy / Shutterstock
Strict containment measures have allowed China to reduce the impact of the first wave of coronavirus infections 2019 (COVID-19). However, in early March 2022 there was a widespread outbreak of the Omicron SARS-CoV-2 variant spreading from Shanghai to China.
About the study
In the present study, the researchers described the epidemiological characteristics and transmission dynamics related to the spread of the Omicron SARS-CoV-2 variant.
The team summarized the non-pharmacological interventions (NPI) that were implemented in Shanghai before and during the Omicron outbreak. Prior to the initial rise in Omicron infections, Shanghai was showing a benchmark of NPI against possible outbreaks, such as strict border control, symptom-based surveillance, case isolation, contact tracking, data-based screening. occupation and travel restrictions.
The team also collected the total number of local and imported infections by COVID-19 based on the symptomatic state reported in Shanghai since December 2019 registered by the Shanghai Municipal Health Commission. Lists of SARS-CoV-2 infections were retrieved from publicly available data sources, followed by integration with additional information.
Non-high risk areas were further divided into two categories according to their spatial proximity to high risk regions: (1) moderate risk areas: areas that were adjacent to high risk regions but were not d high-risk areas, and (2) low-risk areas: areas that were not adjacent to high-risk areas and were not classified as high-risk areas.
Results
The results of the study showed that the number of imported COVID-19 infections reached a maximum of 81 cases per day on February 24, 2021, more than 19 times the daily average observed between 2020 and 2021. A total of 1,112 imported cases were observed. between February 15 and March 15, 2021. The team found that among incoming travelers, the test positivity rate was the highest in February 2022, with a maximum of 96.3 infections observed. per 1,000 passengers.
The sudden increase in the number of infected passengers led to a breach of the check-in program. This breach was probably responsible for the high transmission to Omicron in early March. On March 1, 2021, a total of 14 positive people were detected for COVID-19 among those attending a dance event. This eventually caused 6,26,000 COVID-19 infections on May 31, 2022 due to the high transmissibility of Omicron and the delayed discovery of the outbreak.
Almost 96% of all infections were detected among people in quarantine. The proportion of infected individuals identified due to community screening decreased to 13.6% in phase 2, which dropped further to 2.7% in phase 3. On the other hand, the number of SARS-CoV-2 infections that showed symptoms ranged from 15.5% in the phase. From 1 to 9.8% in phase 3.
Approximately 99.5% of Shanghai’s sub-districts reported SARS-CoV-2 infections. However, the team observed a very heterogeneous distribution of infections, with 40% of the city area reporting 80% of all infections, including the Pudong New area which reported 35 .5% of total infections. In addition, the total incidence of reported COVID-19 infections was 0.02 infections per 1,000 people during phase 1, which increased to 2.0 per 1,000 in phase 2 and 21.9 per 1,000 in phase 3.
The propagation rate of COVID-19 slowed steadily from an average of 544 meters per day reported in the first week of the outbreak from February 27 to March 5, 2021 to 325 meters per day from March 25 to 31 March 2021.
Between March 16 and March 29, 2021, the total number of COVID-19 infections reported per 1,000 people was 2.2 in high-risk areas and 1.51 in high-risk areas. moderate and 0.53 in low-risk areas. The team noted that the implementation of intervention strategies prior to the implementation of the blockade across the city did not slow down the increase in infections enough. Overall, the growth rate of COVID-19 transmission in phase 2 was 0.26 per day, while the number of infections doubled every 3.21 days.
Conclusion
Overall, the findings of the study highlighted the risk of COVID-19 outbreaks in China, while the implementation of strict NPIs along with a city-wide blockade could effectively control the outbreak of SARS-CoV- 2 Omicron. Researchers believe that studying the impact of each intervention could help to better understand key public health priorities.
* Important news
medRxiv publishes preliminary scientific reports that are not peer-reviewed and therefore should not be considered conclusive, guided by clinical practice or health-related behavior, or treated as established information.