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A preprint, an unpublished non-peer reviewed paper posted on medRxiv, has looked at links between weather and severity of COVID-19 cases.
Dr François Cohen, environmental economist with expertise in the impact of the weather on socioeconomic factors, and postdoctoral researcher, Institute for New Economic Thinking at the Oxford Martin School and Smith School of Enterprise and the Environment, University of Oxford, said:
“The decrease in hospitalization times found in this paper are very interesting. However, the conclusion that seasonality would be the main driver of this change is interpretative.
“The authors clearly mention that there are strong limitations to their analysis: ‘Potential sampling bias is the main limitation of this study […] we still cannot exclude the possibility that some other unidentified external factors (including confinement and social distancing, improvement and compliance of prevention and environmental hygiene protocols and even decreased air-pollution could have progressively affected the severity of patients arriving to the hospital) were affecting composition of hospitalized patient cohorts and contributing to the decreased COVID-19 severity and mortality.’
“I believe that many confounding factors could explain the decrease in hospitalisation times, beyond the weather, and would therefore recommend being very cautious when mentioning the results of this study.
“We are working on a paper looking at the difficulties of estimating an impact of the weather on the spread of COVID-19, which will be published shortly, and which we are happy to share under embargo.”
Dr Simon Clarke, Associate Professor of Cellular Microbiology at the University of Reading, said:
“We don’t currently know whether Covid-19 cases have any association with the seasons. On the one hand we have a current, summer outbreak in the United States but we’ve also seen an unusual number of infections occur in workplaces where cold conditions occur, which is well established as being association with colds and flu.
“This study shows an association between temperature and severity of symptoms, but it does not demonstrate why that happens. It may be because low temperatures slow down the normal mucus clearing of infecting viruses in our nasal passages.
“If there is indeed a wave of infections in the UK this winter, it could coincide with the annual flu season, which itself puts significant stress on the NHS. We could experience a double-whammy of serious respiratory diseases, which could cause the NHS to grind to a halt. It’s essential that the government mount an extensive publicity campaign to ensure that uptake of this year’s flu vaccination is as extensive as possible.”
Dr Shaun Fitzgerald FREng, Royal Academy of Engineering Visiting Professor at the University of Cambridge, said:
“The press release says ‘Additionally, very dry indoor environments created by air conditioning in hot countries (such as in the Southern US) could also contribute to the severity of the disease – a hypothesis that needs further investigation’ – however, air conditioning systems tend to have a recommended range of humidity (a range 40-60% would not be uncommon as a recommendation), so any air-conditioning system which creates relative humidity conditions outside of the recommended range should probably be examined anyway for reasons of comfort, irrespective of the current crisis. Completely apart from the COVID-19 situation, occupants can develop itchy eyes, dry skin etc. if air-conditioned buildings aren’t well maintained or are poorly designed. But many buildings I have seen are in fact looked after properly with appropriate air conditioning.”
Prof Rowland Kao, Sir Timothy O’Shea Professor of Veterinary Epidemiology and Data Science, University of Edinburgh, said:
“This paper has not yet been peer reviewed, and thus its conclusions should be viewed with the caution we would take with any preprint. Should its results hold, then this represents an important outcome – namely, showing that in a variety of settings, there is strong evidence for an increase in severity of COVID-19 with lowered temperature and increased humidity as would be associated with the winter months in temperate climates, and as is common in other respiratory infections such as seasonal influenza.
“As this paper only looks at hospitalisations (and therefore severe cases and deaths) it does not address the question of whether or not COVID-19 would transmit more readily in those conditions, and therefore it should not be inferred that the result would be a larger epidemic.
“A further caveat, is that it is difficult to assess whether any decline in deaths or severity over time is associated with improved methods for in-hospital treatment over time, and as staff become more experienced in working with COVID-19 cases, and/or as numbers of infected fall off over time (reducing strain on hospital staff).
“Also not explored is the potential role for co-morbidities, if for example the attack rate of COVID-19 is higher in individuals whose health is already compromised as, if true, this would mean that many of those more likely to be severely affected would also be more likely to be infected earlier.
“While these cautionary notes suggest that further work is needed to be sure of the impact of temperature and humidity on COVID-19 mortality and severity, it is an important dataset, as any increase in severity and mortality would not only be a tragedy for those who are affected, but also place additional burdens on our health care systems as we anticipate both new outbreaks and a potential second wave of COVID-19 infections over the coming months.”
Preprint: ‘Effects of environmental factors on severity and mortality of COVID-19’ by Domagoj Kifer et al. This work is not peer-reviewed.
https://www.medrxiv.org/content/10.1101/2020.07.11.20147157v2
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