Summer in the Northern Hemisphere has come and gone – and while we fire up our barbeques a few more times before autumn brings back the cold, COVID-19 is far from being gone.
This might come as a surprise to some, as a plethora of pre-print studies have claimed that rising temperatures would slow the spread of COVID-19. News of such studies, typically not peer-reviewed, even made it as far as President Trump, who famously claimed the virus would be all but gone come Summer 2020. Instead, cases in the United States have soared over the summer despite the high temperatures.
Oxford researchers, led by Dr. Francois Cohen and including Climate Econometrics’ Moritz Schwarz, have published a new analysis in Environmental and Resource Economics examining the challenge of using epidemiological case count data.
COVID-19 has posed a considerable challenge for scientists who have been scrambling to understand this new disease. At the start of the global pandemic, testing for most countries was slow and while it has increased in many places, it remains insufficient in others. Less testing means less data, which in turn makes it difficult to understand exactly what is driving the disease.
While it made sense to a priori assume that COVID-19 could spread more easily in cold weather, given that some other respiratory illnesses do, this new analysis suggests that such a conclusion is difficult (if not impossible) to draw at this moment.
Symptoms for COVID-19 resemble those of other respiratory illnesses, such as the common cold and flu. We know that these diseases are affected by weather conditions. The likelihood is that the variation in other respiratory illnesses caused by changing weather could lead to variation in COVID-19 testing frequency, resulting in some distortions in the prevalence estimates of COVID-19. This makes it impossible to estimate the true influence of the weather on the spread of the virus.
The problem with studies that seek to tie the severity or spread of the disease to any one factor is they risk drawing incomplete conclusions. The spread of COVID-19 is affected by a host of variables, and to disentangle the many potential influences is very difficult. As many studies are already being used to decide policy, one major concern is that they could pose a considerable risk to the public if their findings are found to be inaccurate.
While there is no quick fix, there are ways to improve the situation by gathering more comprehensive and reliable data, such as randomly sampling sections of the population, as the Office for National Statistics in the UK has started doing. Until our understanding of the disease has improved, it is important to be cautious of claims that there is a relationship between any one factor and the spread of COVID-19.
Given the uncertainty about what can affect the spread of COVID-19, the safest option is to exercise caution and maintain appropriate social distancing and hygiene while enjoying whatever is left of the good weather this autumn.
 Cohen, F., Schwarz, M., Li, S., Lu, Y. & Jani, A. (2020) “The Challenge of Using Epidemiological Case Count Data: The Example of Confirmed COVID19 Cases and the Weather”, Perspectives on the Economics of the Environment in the Shadow of Coronavirus, Environment and Resource Economics
Angela Wenham, Centre Manager, Nuffield College
Moritz Schwarz, DPhil Student, Department of Geography