Yang Guo Jing, Song Haolong, Lim Jue Tao, Janhavi A, Gan Gregory, Tong Guan, Ma Pei, Lim Wei Han Nigel, Bin Mohd Aziz Muhammad Hafiz, Dickens Borame L
Saw Swee Hock School of Public Health, National University of Singapore, Singapore.
Lee Kong Chian School of Medicine, Nanyang Technological University, Singapore.
Infect Dis Model. 2025 Jul 20;10(4):1398-1417. doi: 10.1016/j.idm.2025.07.008. eCollection 2025 Dec.
Yellow Fever (YF) importation remains an active risk to Southeast Asia. This study aims to determine the effectiveness of vector control and ring vaccination as containment strategies.
We modelled a YF outbreak in Singapore over 1 year using a metapopulation vector-host spatial model to explore the impact of a potential epidemic and intervention effectiveness. 30 different scenarios were examined by varying the vector to human ratio ([1, 3, 6]), vaccination coverage ([10 %, 50 %, 90 %]) and delay in vaccine rollout ([7, 14, 30 days]), including three non-vaccination scenarios with the vector-to-human ratio m ([1, 3, 6]).
Vector control has a significant protective effect with an 89 % reduction in the cumulative number of exposed cases at Day 365 when lowering from 6 to 1 in the baseline scenario without ring vaccination. Vaccination coverage levels of 90 %, 50 %, and 10 % reduce the cumulative number of exposed cases by 88 %, 56 %, and 12 %, respectively, compared to baseline, when fixing m = 3 and a 7-day rollout delay. A greater number of severe infections and deaths can be mitigated by decreasing the ratio m compared to ring vaccination strategies. The marginal gains in averting the number of infections and deaths are most significant when m is decreased, followed by increased vaccination coverage and reduced intervention delay as R is proportional to . This highlights the central role of vector control. Our findings suggested that ring vaccination is effective under lower mosquito-to-human ratios up to 1-week post-detection, with vaccination coverage of at least 50 %. Under these settings, vaccine doses equal to 25 % of the total population are needed to contain the initial outbreak, allowing time to monitor its progress and restock the supply. After that, further interventions where YF has not yet been declared endemic.
Our findings suggested that ring vaccination is effective under lower mosquito-to-human ratios up to 1-week post-detection, with vaccination coverage of at least 50 %. After that, further interventions are required to bring the effective reproduction number under 1, highlighting the need for rapid response and containment, preparation in the stockpiling of vaccines, and continual suppression of mosquito vector populations when faced with the risk of YF importation and outbreak.
黄热病（YF）输入仍是东南亚面临的一项现实风险。本研究旨在确定病媒控制和环状疫苗接种作为遏制策略的有效性。
我们使用异质种群病媒-宿主空间模型对新加坡一年内的黄热病疫情进行建模，以探讨潜在疫情的影响和干预效果。通过改变病媒与人类的比例（[1, 3, 6]）、疫苗接种覆盖率（[10%、50%、90%]）以及疫苗推出延迟时间（[7、14、30天]），研究了30种不同的情景，包括三种无疫苗接种情景，病媒与人类的比例为m（[1, 3, 6]）。
在无环状疫苗接种的基线情景下，当病媒与人类的比例从6降至1时，病媒控制具有显著的保护作用，在第365天时暴露病例的累积数量减少了89%。当固定m = 3且疫苗推出延迟7天时，与基线相比，疫苗接种覆盖率达到90%、50%和10%时，暴露病例的累积数量分别减少了88%、56%和12%。与环状疫苗接种策略相比，降低比例m可减轻更多的严重感染和死亡。当m降低时，避免感染和死亡人数的边际收益最为显著，其次是提高疫苗接种覆盖率和缩短干预延迟时间，因为R与 成正比。这突出了病媒控制的核心作用。我们的研究结果表明，在检测后长达1周的较低蚊媒与人类比例情况下，环状疫苗接种是有效的，疫苗接种覆盖率至少为50%。在这些情况下，需要相当于总人口25%的疫苗剂量来控制初始疫情，以便有时间监测疫情进展并补充供应。之后，在黄热病尚未宣布为地方病的情况下需要采取进一步干预措施。
我们的研究结果表明，在检测后长达1周的较低蚊媒与人类比例情况下，环状疫苗接种是有效的，疫苗接种覆盖率至少为50%。之后，需要采取进一步干预措施将有效繁殖数R降至1以下，这凸显了面对黄热病输入和疫情风险时快速应对和遏制、储备疫苗以及持续抑制蚊媒数量的必要性。
