International Journal of Environmental Research and Public Health Review Winter Is Coming: A Southern Hemisphere Perspective of the Environmental Drivers of SARS-CoV-2 and the Potential Seasonality of COVID-19 Albertus J. Smit 1,2,* , Jennifer M. Fitchett 3 , Francois A. Engelbrecht 4, Robert J. Scholes 4 , Godfrey Dzhivhuho 5 and Neville A. Sweijd 6 1 Department of Biodiversity and Conservation Biology, University of the Western Cape, Cape Town 7535, South Africa 2 Elwandle Coastal Node, South African Environmental Observation Network (SAEON), Port Elizabeth 6031, South Africa 3 School of Geography, Archaeology and Environmental Studies, University of the Witwatersrand, Johannesburg 2050, South Africa; [email protected] 4 Global Change Institute, University of the Witwatersrand, Johannesburg 2050, South Africa; [email protected] (F.A.E.); [email protected] (R.J.S.) 5 Department of Microbiology, Immunology and Cancer Biology, Myles H. Thaler Center for AIDS and Human Retrovirus Research, University of Virginia, Charlottesville, VA 22903, USA; [email protected] 6 Alliance for Collaboration on Climate and Earth Systems Science (ACCESS), Council for Scientific and Industrial Research (CSIR), Pretoria 0001, South Africa; [email protected] * Correspondence: [email protected] Received: 1 June 2020; Accepted: 31 July 2020; Published: 5 August 2020 Abstract: 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. Int. J. Environ. Res. Public Health 2020, 17, 5634; doi:10.3390/ijerph17165634 www.mdpi.com/journal/ijerph Int. J. Environ. Res. Public Health 2020, 17, 5634 2 of 28 Keywords: COVID-19; environmental influences; humidity; SARS-CoV-2; seasonality; temperature Int. J. Environ. Res. Public Health 2020, 17, x 2 of 29 1.1. Introduction Introduction AA novel novel coronavirus, coronavirus, thought thought to to have have made made a a zoonotic zoonotic transition transition from from bats, bats, infected infected a a human human hosthost in in Wuhan, Wuhan, Hubei Province, China [[1].1]. By late January 2020,2020, thethe virus,virus, newlynewly namednamed SARS-CoV-2, SARS‐CoV‐ 2,and and the the disease disease it causes, causes, COVID COVID-19,‐19, had had spread spread to 18 to other 18 other Chinese Chinese provinces, provinces, and to and Japan, to South Japan, Korea,South Korea,Taiwan, Taiwan, Thailand, Thailand, and the and USA. the On USA. the On date the of date submission of submission of this ofreview this review (15 July (15 2020), July 2020),there werethere 13,331,879 were 13,331,879 confirmed confirmed cases, in cases, virtually in virtually every country every worldwide country worldwide (213 countries (213 and countries territories, and Figureterritories, 1). At Figure the 1time,). At it the was time, reported it was reportedthat 577,825 that 577,825people peopleinfected infected with the with virus the had virus died; had died;both numbersboth numbers have havesubsequently subsequently risen. risen. The The only only comparable comparable acute acute respiratory respiratory disease disease pandemic pandemic was was SpanishSpanish InfluenzaInfluenza (H1N1),(H1N1), transmitted transmitted from from birds birds to peopleto people in 1918,in 1918, which which lasted lasted until until 1919 and1919 killed and killedan estimated an estimated 50 million 50 million people people worldwide. worldwide. In the current In the highlycurrent interconnected highly interconnected world, the world, impact the of impactthe COVID-19 of the COVID pandemic‐19 pandemic is likely to is be likely felt for to many be felt years for many [2–4]. years It is therefore [2–4]. It is crucial therefore that allcrucial potential that alldeterminants potential ofdeterminants the rate and locationof the rate of the and pandemic location spread of the receive pandemic careful considerationspread receive in ordercareful to considerationmake appropriate in order plans to for make its management.appropriate plans for its management. FigureFigure 1. 1. TheThe number number of of confirmed confirmed COVID COVID-19‐19 cases cases as as of of 12 12 July July 2020. 2020. Data Data are are shown shown as as the the number number ofof cases cases per per 100,000 100,000 individuals. individuals. COVID COVID-19‐19 case case data data are are from from Johns Johns Hopkins Hopkins University University Center Center for for SystemsSystems Science Science and and Engineering. Engineering. The The world world population population data data are are from from the the World World Bank. EpidemiologicalEpidemiological models havehave been been used used worldwide worldwide to to guide guide the the imposition imposition (or (or not) not) of policy of policy and andregulatory regulatory intervention intervention [5,6]. These [5,6]. models These canmodels be modified can be to modified include aspects to include of social aspects characteristics of social of characteristicsthe infected populations; of the infected and they populations; can also be and adapted they can to reflect also thebe adapted modulating to reflect effect ofthe environmental modulating effectinfluences of environmental on the processes influences that determine on the processes transmission. that determine transmission. ManyMany relatedrelated respiratory respiratory diseases diseases show show a connection a connection between between climate climate variables variables and the dynamicsand the dynamicsof the disease. of the It disease. is thus plausible It is thus that plausible such a that dependency such a dependency could exist forcould SARS-CoV-2 exist for SARS (reviewed‐CoV‐ in2 (reviewedSection4). in Given Section that 4). the Given COVID-19 that the outbreak COVID‐ began19 outbreak in mid-winter began in in mid the‐winter northern in the hemisphere, northern hemisphere,where it was where (at the it time was of(at writing) the time peaking of writing) toward peaking the middle toward of the the middle boreal of summer, the boreal and summer, that the andopposite that the scenario opposite seems scenario to be playingseems to out be playing in many out southern in many hemisphere southern hemisphere countries, it countries, is tempting it is to temptingassociate thisto associate pattern with this climate pattern seasonality, with climate as manyseasonality, publications as many have publications suggested. However, have suggested. it is also However,plausible thatit is thealso association plausible that is spurious, the association related simplyis spurious, to coincidental related simply spatial to connectivity coincidental between spatial connectivitycountries. It isbetween necessary countries. to critically It is assess necessary the evidence to critically for environmental assess the evidence sensitivity, for in environmental both the virus sensitivity,and the disease, in both before the virus arriving and atthe conclusions disease, before that mayarriving have at significant conclusions implications. that may have significant implications. In terms of a response to the pandemic, we need to understand whether and how environmental variables influence the infection rate. This knowledge provides clues for policy and practice to reduce the spread of the virus and potential for treatment options. For example, if analyses show that absolute humidity is strongly associated with reduced