SARS-CoV-2 virus infections in humans were first reported in December 2019, the boreal winter. The resulting COVID-19 pandemic was declared by the WHO in March 2020. By July 2020, COVID-19 was present in 213 countries and territories, with over 12 million confirmed cases and over half a million attributed deaths. Knowledge of other viral respiratory diseases suggests that the transmission of SARS-CoV-2 could be modulated by seasonally varying environmental factors such as temperature and humidity. Many studies on the environmental sensitivity of COVID-19 are appearing online, and some have been published in peer-reviewed journals. Initially, these studies raised the hypothesis that climatic conditions would subdue the viral transmission rate in places entering the boreal summer, and that southern hemisphere countries would experience enhanced disease spread. For the latter, the COVID-19 peak would coincide with the peak of the influenza season, increasing misdiagnosis and placing an additional burden on health systems. In this review, we assess the evidence that environmental drivers are a significant factor in the trajectory of the COVID-19 pandemic, globally and regionally. We critically assessed 42 peer-reviewed and 80 preprint publications that met qualifying criteria. Since the disease has been prevalent for only half a year in the northern, and one-quarter of a year in the southern hemisphere, datasets capturing a full seasonal cycle in one locality are not yet available. Analyses based on space-for-time substitutions, i.e., using data from climatically distinct locations as a surrogate for seasonal progression, have been inconclusive. The reported studies present a strong northern bias. Socio-economic conditions peculiar to the ‘Global South’ have been omitted as confounding variables, thereby weakening evidence of environmental signals. We explore why research to date has failed to show convincing evidence for environmental modulation of COVID-19, and discuss directions for future research. We conclude that the evidence thus far suggests a weak modulation effect, currently overwhelmed by the scale and rate of the spread of COVID-19. Seasonally modulated transmission, if it exists, will be more evident in 2021 and subsequent years.

中文翻译：

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冬天即将来临：南半球对 SARS-CoV-2 环境驱动因素和 COVID-19 潜在季节性的看法。

人类 SARS-CoV-2 病毒感染首次报道于 2019 年 12 月，即北方的冬季。世界卫生组织于 2020 年 3 月宣布由此引发的 COVID-19 大流行。截至 2020 年 7 月，COVID-19 已遍布 213 个国家和地区，确诊病例超过 1200 万例，死亡病例超过 50 万例。对其他病毒性呼吸道疾病的了解表明，SARS-CoV-2 的传播可以通过季节性变化的环境因素（例如温度和湿度）来调节。许多关于 COVID-19 环境敏感性的研究出现在网上，其中一些已发表在同行评审的期刊上。最初，这些研究提出了这样的假设：气候条件会抑制进入北方夏季的地区的病毒传播率，而南半球国家的疾病传播将会加剧。对于后者来说，COVID-19 高峰期将与流感季节高峰期同时发生，从而增加误诊率并给卫生系统带来额外负担。在本次综述中，我们评估了环境驱动因素是全球和区域性 COVID-19 大流行轨迹的重要因素的证据。我们严格评估了 42 份经过同行评审的出版物和 80 份符合资格标准的预印本出版物。由于该疾病在北半球仅流行半年，而在南半球仅流行四分之一年，因此尚无法获取某个地区完整季节周期的数据集。基于空间-时间替代的分析，即使用来自气候不同地点的数据作为季节进展的替代，尚未得出结论。报告的研究呈现出强烈的北方偏见。“南半球”特有的社会经济条件作为混杂变量被忽略，从而削弱了环境信号的证据。我们探讨了为什么迄今为止的研究未能显示出有关 COVID-19 环境调节的令人信服的证据，并讨论了未来研究的方向。我们的结论是，迄今为止的证据表明调制效应较弱，目前已被 COVID-19 传播的规模和速度所压倒。季节性调制传输（如果存在）将在 2021 年及随后几年更加明显。