此中國研究發現，北京、上海、深圳及溫州的第一波疫情，在積極採取多項管制措施後，新冠病毒「即時有效繁殖率」( instantaneous reproduction number，Rt) 逐漸降到1以下，表示疫情已受控制。作者進一步利用傳染病模型(Susceptible–Infectious–Recovered, SIR model)預測發現，處在境外移入病例增加的第二波疫情中，即使剛始是病例數不多的小規模疫情，但若逐漸鬆綁管制措施，病例數將會呈指數型快速上升; 雖然在再次採取嚴厲的管控措施下，疫情可以得到控制，但過程中會付出相當的健康及經濟的損失。因此如何在社經活動及疫情管控兩者間取得平衡，是重要的課題。作者建議 Rt可以當作決策的重要指標，在新冠疫苗上市前，決策單位應參考動態的Rt，微調各項管制政策，儘可能將Rt維持在1以下，避免疫情再次的爆發。
註: 「即時有效繁殖率」( instantaneous reproduction number，Rt)的定義為一個個案發病後，在 t時間點平均可以傳給幾個人。Rt < 1 表示疫情逐漸控制中; Rt > 1 表示疫情仍持續流行。 會影響Rt的因子包含:人口密度、交通運輸、個人防護、社經活動、病毒傳播能力等。
As of March 18, 2020, 13 415 confirmed cases and 120 deaths related to coronavirus disease 2019 (COVID-19) in mainland China, outside Hubei province—the epicentre of the outbreak—had been reported. Since late January, massive public health interventions have been implemented nationwide to contain the outbreak. We provide an impact assessment of the transmissibility and severity of COVID-19 during the first wave in mainland Chinese locations outside Hubei.
We estimated the instantaneous reproduction number (Rt) of COVID-19 in Beijing, Shanghai, Shenzhen, Wenzhou, and the ten Chinese provinces that had the highest number of confirmed COVID-19 cases; and the confirmed case-fatality risk (cCFR) in Beijing, Shanghai, Shenzhen, and Wenzhou, and all 31 Chinese provinces. We used a susceptible–infectious–recovered model to show the potential effects of relaxing containment measures after the first wave of infection, in anticipation of a possible second wave.
In all selected cities and provinces, the Rt decreased substantially since Jan 23, when control measures were implemented, and have since remained below 1. The cCFR outside Hubei was 0·98% (95% CI 0·82–1·16), which was almost five times lower than that in Hubei (5·91%, 5·73–6·09). Relaxing the interventions (resulting in Rt >1) when the epidemic size was still small would increase the cumulative case count exponentially as a function of relaxation duration, even if aggressive interventions could subsequently push disease prevalence back to the baseline level.
The first wave of COVID-19 outside of Hubei has abated because of aggressive non-pharmaceutical interventions. However, given the substantial risk of viral reintroduction, particularly from overseas importation, close monitoring of Rt and cCFR is needed to inform strategies against a potential second wave to achieve an optimal balance between health and economic protection.
Author：Leung K, Wu JT, Liu D, et al.