2021年5月至8月大臺北地區新冠疫情期間三級警戒 與社區採檢成效：數理模式分析

Abstract

背景：2021年5月大臺北地區爆發與茶室相關SARS-CoV-2 Alpha變異株社區疫情。政府迅速實施三級疫情警戒以落實口罩配戴並避免非必要社交接觸，同時提供以症狀為基礎的社區採檢服務，但並未封城（限制人民移動）。疫情迅速受控並在8月底歸零，但防疫措施成效迄今仍未有評估。本研究旨在分析三級警戒及社區採檢在控制此波大臺北地區SARS-CoV-2疫情的角色。

方法：本研究建構具高低風險群結構並考慮口罩配戴、採檢隔離及疫苗接種效果的SARS-CoV-2動態傳播模型，擬合大臺北地區2021年5月4日至8月31日間確診病例數流行曲線。以未實施三級警戒及社區採檢之虛擬反事實情境為基準估計這兩項措施對於確診人數與感染人數的預防百分比。並針對與人接觸時高風險群口罩配戴率、高風險群接觸者追蹤率、低風險族群接觸者追蹤率、與同質混合傳播係數等四項參數進行敏感度分析。

結果：模型擬合結果顯示：高風險群佔大臺北地區人口約0·4% (約42,000人)。SARS-CoV-2 Alpha變異株基本再生數 (R0) 在高風險群為6·26，在低風險群則為0·23。估計79·1%確診病例為高風險群。單獨實施疫情警戒可預防29·1% (25·0%-33·6%) 確診人數及34·8% (30·6%-39·1%) 感染人數，單獨實施社區採檢會預防2·4% (1·1%-3·5%) 確診人數及 14·2% (13·6%-14·4%) 感染人數。兩者共同實施則有協同效應，防止46·2% (42·6%-50·5%) 確診人數及56·5% (53·0%-60·1%) 感染人數。敏感度分析顯示在參數不確定性範圍內，兩項防疫措施均有協同作用。

闡釋：同時實施三級警戒和社區採檢兩項防疫措施有效控制2021年大臺北地區SARS-CoV-2 Alpha變異株疫情，且兩者間具有協同作用。

Background: In May 2021, Taiwan faced its first community outbreak of the SARS-CoV-2 Alpha variant, linked to teahouses in Taipei metropolitan area. In response, the government swiftly implemented non-lockdown epidemic alert (enforcing surgical mask wearing without movement restriction) and symptom-based community testing service. By the end of August, the epidemic was effectively controlled. However, the effect of these measures has not yet been evaluated. This modelling study aims to estimate the impact of non-lockdown epidemic alert and symptom-based community testing on the SARS-CoV-2 epidemic in Taipei metropolitan area.

Methods: We constructed a deterministic, risk-structured SARS-CoV-2 compartmental model, considering the effect of mask wearing, testing-contact tracing-quarantine and vaccination program, and fitted it to the daily new diagnosed cases from May 4, 2021 to August 31, 2021. The percentage of cases prevented by non-lockdown epidemic alert and symptom-based community testing was evaluated by calculating the percentage reduction in cumulative cases compared to counterfactual scenario without these measures. Sensitivity analysis with four parameters: the proportion of individuals adhering to masking among high-risk individuals, the initial proportion of contact tracing among high-risk and low-risk individuals, and the assortative mixing of the transmission coefficient.

Findings: Model fitting revealed that high-risk individuals constitute 0·4% (approximately 42,000) of the population in the Taipei metropolitan area, with a basic reproductive number (R0) of 6·26 and 0·23 for high-risk and low-risk individuals, respectively. It is estimated that 79·1% of diagnosed cases originated from the high-risk group. The non-lockdown epidemic alert alone could prevent 29·1% (25·0%-33·6%) of diagnosed cases and 34·8% (30·6%-39·1%) of infected cases, while symptom-based community testing alone could prevent 2·4% (1·1%-3·5%) of diagnosed cases and prevent 14·2% (13·6%-14·4%) of infected cases. The combination of both interventions provided a synergistic effect, preventing 46·2% (42·6%-50·5%) of diagnosed cases and 56·5% (53·0%-60·1%) of infected cases. Sensitivity analysis demonstrated that the synergistic effect remains robust under the uncertainty of parameters.

Interpretation: Simultaneously implementing the epidemic alert and community testing effectively and successfully controlled the SARS-CoV-2 epidemic in Taipei metropolitan area in 2021, demonstrating a synergistic effect.