Instantaneous reproduction number key in determining ability to relax COVID-19 restrictions

1. Following aggressive interventions across China since January 23, 2020, the confirmed case fatality risk in mainland China was 0.98%, five times smaller than that of Hubei, the epicenter of the COVID-19 spread.

 2. Relaxing restrictions and allowing the instantaneous reproduction number to rise above 1, even if restrictions were subsequently tightened, would likely still result in health and economic losses. 

Evidence Rating Level: 3 (Average)

Mainland China has observed 13,415 confirmed cases of COVID-19 and 120 deaths as of March 18, 2020. This is outside the epicenter of the virus outbreak in Hubei province. Massive non-pharmacological interventions were implemented across the country to reduce the spread, including a lockdown of Wuhan since January 23, 2020 along with 16 neighboring cities. This study provided an impact assessment of the severity and transmissibility of COVID-19 during the first wave in four cities (confirmed cases): Beijing (411), Shanghai (337), Shenzhen (417), and Wenzhou (504). Further, a susceptible-infectious-recovered model was used to simulate the potential effects of relaxing the interventions following the first wave. An instantaneous reproduction number (Rt) of COVID-19 was defined as the average number of secondary cases that one primary case could generate and derived from various databases from each city. Rt substantially decreased following the implementation of aggressive measures, keeping it steadily below 1. The confirmed case-fatality risk (cCFR) outside Hubei was 0.98% (95% CI 0.82 to 1.16), though the authors noted substantial heterogeneity across provinces such as Hubei (cCFR 5.91%, 95% CI 5.73 to 6.09) due to variable economies and healthcare resources. A susceptible-infectious-recovered model was used to simulate the potential effects of relaxing the interventions following the first wave. It was found that mainland China is capable of doing so very slowly, such that Rt will not exceed 1. As Rt is a function of time, quick relaxation of interventions or continuation of relaxation when the threshold had been breached resulted in a severe and exponential rise in COVID-19 cases. Relaxation should only be considered when the Rt is consistently <1 and can be kept at that level. Overall, the authors provide a basis upon which other countries with rising cases can learn, including not only aggressive measures to thwart the spread of the virus but very careful and slow relaxation of these interventions when the first wave subsides.

Click to read the study in Lancet

Image: PD

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