Evidence of initial success for China exiting COVID-19 social distancing policy after achieving containment

Abstract

Background: The COVID-19 epidemic was declared a Global Pandemic by WHO on 11 March 2020. By 24 March 2020, over 440,000 cases and almost 20,000 deaths had been reported worldwide. In response to the fast-growing epidemic, which began in the Chinese city of Wuhan, Hubei, China imposed strict social distancing in Wuhan on 23 January 2020 followed closely by similar measures in other provinces. These interventions have impacted economic productivity in China, and the ability of the Chinese economy to resume without restarting the epidemic was not clear. Methods: Using daily reported cases from mainland China and Hong Kong SAR, we estimated transmissibility over time and compared it to daily within-city movement, as a proxy for economic activity. Results: Initially, within-city movement and transmission were very strongly correlated in the five mainland provinces most affected by the epidemic and Beijing. However, that correlation decreased rapidly after the initial sharp fall in transmissibility. In general, towards the end of the study period, the correlation was no longer apparent, despite substantial increases in within-city movement. A similar analysis for Hong Kong shows that intermediate levels of local activity were maintained while avoiding a large outbreak. At the very end of the study period, when China began to experience the re-introduction of a small number of cases from Europe and the United States, there is an apparent up-tick in transmission. Conclusions: Although these results do not preclude future substantial increases in incidence, they suggest that after very intense social distancing (which resulted in containment), China successfully exited its lockdown to some degree. Elsewhere, movement data are being used as proxies for economic activity to assess the impact of interventions. The results presented here illustrate how the eventual decorrelation between transmission and movement is likely a key feature of successful COVID-19 exit strategies.

Keywords: COVID-19; exit strategy; social distancing; transmission.

Figure 1.. Plots of daily new confirmed cases (red line, top row) and daily movement index (Exante Data Inc, NY, bottom row) for Hubei, Beijing, Guangdong, Henan, Hunan, and Zhejiang in 2019 (light blue) and 2020 (dark blue).

Daily new confirmed cases are shown by report date. Movement data in 2019 have been adjusted so that the first day of Lunar New Year in 2019 is assumed to be on the same Gregorian date as 2020. The cyclic movement patterns seen in Beijing and toward the end of February in Zhejiang are the result of decreased travel on weekends.

Figure 2.. Plots of estimated reproduction number, movement, and correlation in the five provinces in mainland China with the highest numbers of cumulative confirmed cases and Beijing (top: Beijing, Guangdong, Henan; bottom: Hubei, Hunan, Zhejiang).

Blue: mean daily movement index (Exante Data Inc, NY), green: mean effective reproduction number estimated using daily confirmed case reports (green shading: 95% credible interval), purple: local correlation between movement index and effective reproduction number. Reproduction number was estimated assuming a lag of -4 days. Dashed lines indicate the upper and lower bounds of the correlation coefficients (-1, 1).

Figure 3.

( A) Plots of daily new confirmed cases (top, red line) and daily movement index (bottom) for Hong Kong in 2019 (light blue) and 2020 (dark blue). Daily new confirmed cases are shown by report date. Movement data in 2019 have been adjusted so that the first day of Lunar New Year in 2019 is assumed to be on the same Gregorian date as 2020. The cyclic movement patterns are the result of decreased travel on weekends. ( B) Plots of estimated reproduction number, movement, and correlation in Hong Kong. Dark blue: mean daily movement index, green: mean effective reproduction number estimated using daily confirmed case reports (green shading: 95% credible interval), purple: local correlation between movement index and effective reproduction number. Dashed lines indicate the upper and lower bounds of the correlation coefficients (-1, 1).