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Abstract：
Objectives The first COVID-19 pandemic waves in many low-income countries appeared milder than initially forecasted. We conducted a country-level ecological study to describe patterns in key SARS-CoV-2 outcomes by country and region and explore associations with potential explanatory factors, including population age structure and prior exposure to endemic parasitic infections. Methods We collected publicly available data and compared them using standardisation techniques. We then explored the association between exposures and outcomes using random forest and linear regression. We adjusted for potential confounders and plausible effect modifications. Results While mean time-varying reproduction number was highest in the European and Americas regions, median age of death was lower in the Africa region, with a broadly similar case-fatality ratio. Population age was strongly associated with mean (β=0.01, 95% CI, 0.005, 0.011) and median age of cases (β=-0.40, 95% CI, -0.53, -0.26) and deaths (β= 0.40, 95% CI, 0.17, 0.62). Conclusions Population age seems an important country-level factor explaining both transmissibility and age distribution of observed cases and deaths. Endemic infections seem unlikely, from this analysis, to be key drivers of the variation in observed epidemic trends. Our study was limited by the availability of outcome data and its causally uncertain ecological design.
摘要：
目标许多低收入国家的第一波COVID-19大流行浪潮似乎比最初预测的要温和。我们进行了一项国家级生态研究，以描述按国家和地区划分的SARS-CoV-2关键结果的模式，并探索与潜在解释因素的关联。包括人口年龄结构和先前暴露于地方性寄生虫感染。方法我们收集了公开可用的数据，并使用标准化技术进行了比较。然后，我们使用随机森林和线性回归探索暴露与结果之间的关联。我们调整了潜在的混杂因素和合理的效果修改。结果欧洲和美洲地区的平均时变繁殖数量最高，非洲地区的中位死亡年龄较低，病死率大致相似。人群年龄与病例的平均年龄（β=0.01，95％CI，0.005，0.011）和中位年龄（β=-0.40，95％CI，-0.53，-0.26）和死亡（β=0.40，95％CI，0.17，0.62）密切相关。结论人口年龄似乎是解释观察到的病例和死亡的传播性和年龄分布的重要国家因素。地方性感染似乎不太可能，从这个分析,是观察到的流行趋势变化的关键驱动因素。我们的研究受到结果数据的可用性及其不确定的生态设计的限制。
