Centre d'Etudes Spatiales de la Biosphère, CESBIO/OMP, UMR UPS-CNES-CNRS-IRD-INRAe, Toulouse, France.
Animal Santé Territoires Risques Ecosystèmes, ASTRE/CIRAD, UMR CIRAD-INRAe-University of Montpellier, Montpellier, France.
PLoS Negl Trop Dis. 2022 Sep 16;16(9):e0010735. doi: 10.1371/journal.pntd.0010735. eCollection 2022 Sep.
The epidemic of COVID-19 has shown different developments in Africa compared to the other continents. Three different approaches were used in this study to analyze this situation. In the first part, basic statistics were performed to estimate the contribution of the elderly people to the total numbers of cases and deaths in comparison to the other continents; Similarly, the health systems capacities were analysed to assess the level of underreporting. In the second part, differential equations were reconstructed from the epidemiological time series of cases and deaths (from the John Hopkins University) to analyse the dynamics of COVID-19 in seventeen countries. In the third part, the time evolution of the contact number was reconstructed since the beginning of the outbreak to investigate the effectiveness of the mitigation strategies. Results were compared to the Oxford stringency index and to the mobility indices of the Google Community Mobility Reports. Compared to Europe, the analyses show that the lower proportion of elderly people in Africa enables to explain the lower total numbers of cases and deaths by a factor of 5.1 on average (from 1.9 to 7.8). It corresponds to a genuine effect. Nevertheless, COVID-19 numbers are effectively largely underestimated in Africa by a factor of 8.5 on average (from 1.7 to 20. and more) due to the weakness of the health systems at country level. Geographically, the models obtained for the dynamics of cases and deaths reveal very diversified dynamics. The dynamics is chaotic in many contexts, including a situation of bistability rarely observed in dynamical systems. Finally, the contact number directly deduced from the epidemiological observations reveals an effective role of the mitigation strategies on the short term. On the long term, control measures have contributed to maintain the epidemic at a low level although the progressive release of the stringency did not produce a clear increase of the contact number. The arrival of the omicron variant is clearly detected and characterised by a quick increase of interpeople contact, for most of the African countries considered in the analysis.
新冠疫情在非洲的发展与其他大洲不同。本研究采用了三种不同的方法来分析这种情况。在第一部分中，进行了基本统计分析，以估计老年人在病例和死亡总数中相对于其他大洲的贡献；同样，分析了卫生系统的能力，以评估漏报水平。在第二部分，从病例和死亡的流行病学时间序列（来自约翰霍普金斯大学）中重建了微分方程，以分析 17 个国家的 COVID-19 动态。在第三部分，重建了自疫情爆发以来接触人数的时间演变，以研究缓解策略的有效性。结果与牛津严格指数和谷歌社区流动性报告的流动性指数进行了比较。与欧洲相比，分析表明，非洲老年人比例较低，平均可将病例和死亡总数解释为 5.1 倍（从 1.9 到 7.8）。这是一个真正的影响。然而，由于国家层面卫生系统的薄弱，非洲的 COVID-19 数量实际上被平均低估了 8.5 倍（从 1.7 到 20. 甚至更多）。从地域上看，从病例和死亡动态获得的模型揭示了非常多样化的动态。在许多情况下，动力学是混沌的，包括在动力学系统中很少观察到的双稳态情况。最后，从流行病学观察直接推断出的接触人数显示出短期缓解策略的有效作用。从长期来看，控制措施有助于将疫情保持在低水平，尽管严格措施的逐步放松并没有导致接触人数的明显增加。分析中考虑的大多数非洲国家都明显检测到并描述了奥密克戎变体的到来及其对人际接触的快速增加。
