Speculation is rife that the coming Southern Hemisphere winter may increase the impact of the COVID-19 epidemic in South Africa, a team of the country’s leading environmental scientists has been established to consider the environmental aspects of COVID-19 in the country, including weather, climate and air pollution.
Under the leadership of the Department of Science and Innovation (DSI), the COVID‑19 Environmental Reference Group (CERG) is currently reviewing the literature, which provides plausible evidence that SARS-CoV-2 infection rates are sensitive to certain climate parameters.
The novel coronavirus, or Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2), is the virus responsible for coronavirus disease 2019 (COVID-19).
SARS-CoV-2 has been circulating for less than six months, and the available data regarding environmental influences on the spread of the virus comes largely from the Northern Hemisphere. There are currently almost 100 studies that are exploring the effects of the climate on the virus. Learning can also be gleaned from laboratory studies on SARS-CoV-2 and similar viruses that have spread globally in the past, such as those responsible for severe acute respiratory syndrome (SARS) and Middle East respiratory syndrome (MERS).
According to the available evidence, coronavirus transmission rates in the Northern Hemisphere have shown a relationship to daily average outdoor air temperatures. Transmission may also be curtailed at high humidity levels. There is also an association with UV radiation levels, which may or may not be independent of the temperature effect. In all cases, the data is inconclusive, and climatic factors appear to explain only part – in most cases a small part – of the variation in infection rates from place to place.
SARS-CoV-2 seems to spread at maximum rates when daily temperatures are in the range of 5 to 11 degrees Celsius, while transmission decreases steadily as the temperature rises. However, it is evident that the virus can be transmitted under any climatic conditions – it is only the rate of transmission which is affected, and this rate remains above the level where an epidemic is possible in all observed climates.
We also know, from other countries, that the majority of infections take place indoors. The viability of the virus on indoor surfaces, and suspended in droplets of mucus in the air, is more or less independent of outdoor conditions. The seasonality effect may also be indirect – in cold conditions, people typically congregate indoors in areas of low ventilation; this partly explains why influenza has a predominantly winter prevalence.
In South Africa, it is well known that the influenza season typically falls between April and September, but the current information on the seasonal prevalence of SARS‑CoV‑2 remains speculative.
CERG is investigating how this information translates in the South African context. Preliminary findings, based on historical average winter conditions, are that as South Africa heads into winter, the portion of the risk of SARS‑CoV‑2 transmission which is attributable to climate will rise due to falling temperatures and humidity across most of the country.
South Africa has a spatially diverse climate. The Western Cape typically experiences cold and wet winters, while other parts of the country, to varying degrees, experience cold but dry conditions. What is also important to note is that seasons vary in their nature from year to year, with some winters being colder or warmer, and wetter or drier, than others. It is therefore important both to account for the different regional sub-climates, and to try to predict what kind of winter we can expect this year.
The strength of the climate effect in South Africa is being tested, using data produced by CERG, in at least three local epidemiological models. The best current projections for the north-east of the country show a higher likelihood that the winter will be slightly cooler than the long-term average during autumn, but become slightly warmer than average towards the end of the winter season.
CERG will update these projections regularly and for a wider set of locations, while also considering the possible relationships between COVID-19 morbidity and air quality and pollution. The team is also investigating how the epidemic will manifest over the next few years, or at least until an effective vaccine becomes widely available. Its investigations will also seek to determine whether SARS-CoV-2 and its variants will become one of the family of common viruses with seasonal prevalence.
CERG has participated in a number of global discussions considering the above questions, and is working with experts internationally to share data and approaches to the analysis of environmental influences on the pandemic. The team is advising the epidemiological modelling group of the national Department of Health on these issues, and will commence with a full analysis of the South African situation in this regard once sufficient data is available.
This kind of research is critical as the number of COVID-19 cases in the country continues to rise, with confirmed infections passing the 8 000 mark on 7 May and the death toll climbing to over 160. The DSI has mobilised South Africa’s scientific resources in support of the government’s COVID-19 response, and the establishment of the COVID-19 Environmental Reference Group is just one of a number of projects that the Department and its entities are involved in.
Issued by the Department of Science and Innovation