Biology Department, Center for Infectious Disease Dynamics, Penn State University, University Park, PA, USA.
Abdou Moumouni University, Niamey, Niger.
J R Soc Interface. 2020 Aug;17(169):20200480. doi: 10.1098/rsif.2020.0480. Epub 2020 Aug 26.
Measles is a major cause of child mortality in sub-Saharan Africa. Current immunization strategies achieve low coverage in areas where transmission drivers differ substantially from those in high-income countries. A better understanding of measles transmission in areas with measles persistence will increase vaccination coverage and reduce ongoing transmission. We analysed weekly reported measles cases at the district level in Niger from 1995 to 2004 to identify underlying transmission mechanisms. We identified dominant periodicities and the associated spatial clustering patterns. We also investigated associations between reported measles cases and environmental drivers associated with human activities, particularly rainfall. The annual and 2-3-year periodicities dominated the reporting data spectrum. The annual periodicity was strong with contiguous spatial clustering, consistent with the latitudinal gradient of population density, and stable over time. The 2-3-year periodicities were weaker, unstable over time and had spatially fragmented clustering. The rainy season was associated with a lower risk of measles case reporting. The annual periodicity likely reflects seasonal agricultural labour migration, whereas the 2-3-year periodicity potentially results from multiple mechanisms such as reintroductions and vaccine coverage heterogeneity. Our findings suggest that improving vaccine coverage in seasonally mobile populations could reduce strong measles seasonality in Niger and across similar settings.
麻疹是撒哈拉以南非洲儿童死亡的主要原因。目前的免疫接种策略在传播驱动因素与高收入国家大不相同的地区覆盖率较低。更好地了解麻疹在持续存在麻疹的地区的传播情况，将提高疫苗接种覆盖率并减少正在发生的传播。我们分析了尼日尔从 1995 年到 2004 年的地区层面每周报告的麻疹病例，以确定潜在的传播机制。我们确定了主要的周期性以及相关的空间聚类模式。我们还调查了报告的麻疹病例与与人类活动相关的环境驱动因素（特别是降雨）之间的关联。年度和 2-3 年周期性主导着报告数据谱。年度周期性很强，具有连续的空间聚类，与人口密度的纬度梯度一致，并且随着时间的推移保持稳定。2-3 年周期性较弱，随着时间的推移不稳定，且空间上呈碎片化聚类。雨季与麻疹病例报告的风险较低相关。年度周期性可能反映了季节性农业劳动力迁移，而 2-3 年周期性可能是由于多种机制（如重新引入和疫苗覆盖率差异）造成的。我们的研究结果表明，提高季节性流动人口的疫苗接种覆盖率可能会降低尼日尔和类似环境中麻疹的强季节性。
