Institute for Health Metrics and Evaluation, University of Washington, Population Health Building/Hans Rosling Center, 3980 15th Ave NE, Seattle, WA, 98195, USA.
Medical Care Development International, 8401 Colesville Road Suite 425, Silver Spring, MD, 20910, USA.
Malar J. 2021 Aug 30;20(1):359. doi: 10.1186/s12936-021-03893-x.
Malaria elimination is the goal for Bioko Island, Equatorial Guinea. Intensive interventions implemented since 2004 have reduced prevalence, but progress has stalled in recent years. A challenge for elimination has been malaria infections in residents acquired during travel to mainland Equatorial Guinea. The present article quantifies how off-island contributes to remaining malaria prevalence on Bioko Island, and investigates the potential role of a pre-erythrocytic vaccine in making further progress towards elimination.
Malaria transmission on Bioko Island was simulated using a model calibrated based on data from the Malaria Indicator Surveys (MIS) from 2015 to 2018, including detailed travel histories and malaria positivity by rapid-diagnostic tests (RDTs), as well as geospatial estimates of malaria prevalence. Mosquito population density was adjusted to fit local transmission, conditional on importation rates under current levels of control and within-island mobility. The simulations were then used to evaluate the impact of two pre-erythrocytic vaccine distribution strategies: mass treat and vaccinate, and prophylactic vaccination for off-island travellers. Lastly, a sensitivity analysis was performed through an ensemble of simulations fit to the Bayesian joint posterior probability distribution of the geospatial prevalence estimates.
The simulations suggest that in Malabo, an urban city containing 80% of the population, there are some pockets of residual transmission, but a large proportion of infections are acquired off-island by travellers to the mainland. Outside of Malabo, prevalence was mainly attributable to local transmission. The uncertainty in the local transmission vs. importation is lowest within Malabo and highest outside. Using a pre-erythrocytic vaccine to protect travellers would have larger benefits than using the vaccine to protect residents of Bioko Island from local transmission. In simulations, mass treatment and vaccination had short-lived benefits, as malaria prevalence returned to current levels as the vaccine's efficacy waned. Prophylactic vaccination of travellers resulted in longer-lasting reductions in prevalence. These projections were robust to underlying uncertainty in prevalence estimates.
The modelled outcomes suggest that the volume of malaria cases imported from the mainland is a partial driver of continued endemic malaria on Bioko Island, and that continued elimination efforts on must account for human travel activity.
赤道几内亚比奥科岛的目标是消除疟疾。自 2004 年以来实施的强化干预措施降低了发病率，但近年来进展已停滞。消除疟疾的一个挑战是居民在前往赤道几内亚大陆旅行时感染的疟疾。本文定量分析了离岛对比奥科岛剩余疟疾发病率的影响，并研究了前期红细胞疫苗在进一步消除疟疾方面的潜在作用。
使用基于 2015 年至 2018 年疟疾指标调查（MIS）数据校准的模型模拟比奥科岛的疟疾传播情况，包括详细的旅行史和快速诊断检测（RDT）的疟疾阳性率，以及疟疾发病率的地理空间估计。蚊虫种群密度根据在当前控制水平下的输入率和岛内流动性进行调整，以适应本地传播。然后，利用这些模拟来评估两种前期红细胞疫苗分发策略的影响：大规模治疗和接种疫苗，以及离岛旅行者的预防性接种。最后，通过拟合贝叶斯联合后验概率分布的模拟集合进行敏感性分析。
模拟结果表明，在人口占 80%的城市马拉博，仍存在一些传播的残余，但很大一部分感染是大陆旅行者输入的。在马拉博以外，流行率主要归因于本地传播。当地传播与输入之间的不确定性在马拉博内最低，在马拉博外最高。使用前期红细胞疫苗保护旅行者将比使用疫苗保护比奥科岛居民免受本地传播的影响更大。在模拟中，大规模治疗和接种疫苗的短期效益有限，因为随着疫苗效力的减弱，疟疾流行率会恢复到当前水平。旅行者的预防性接种导致流行率的持续下降。这些预测结果对流行率估计的潜在不确定性具有稳健性。
模型结果表明，从大陆输入的疟疾病例数量是比奥科岛持续发生地方性疟疾的部分驱动因素，消除疟疾的努力必须考虑到人类的旅行活动。
