Abstract: Seasonality and uncertainty in global COVID-19
growth rates
Cory Merowa,b,c,1 and Mark C. Urbanb,c
a
Eversource Energy Center, University of Connecticut, Storrs, CT 06268; bCenter of Biological Risk, University of Connecticut, Storrs, CT 06268;
and cDepartment of Ecology & Evolutionary Biology, University of Connecticut, Storrs, CT 06268
Edited by Nils Chr. Stenseth, University of Oslo, Oslo, Norway, and approved September 16, 2020 (received for review May 1, 2020)
The virus causing COVID-19 has spread rapidly worldwide and
threatens millions of lives. It remains unknown, as of April 2020,
whether summer weather will reduce its spread, thereby alleviating strains on hospitals and providing time for vaccine development. Early insights from laboratory studies and research on
related viruses predicted that COVID-19 would decline with higher
temperatures, humidity, and ultraviolet (UV) light. Using current,
fine-scaled weather data and global reports of infections, we develop a model that explains 36% of the variation in maximum
COVID-19 growth rates based on weather and demography
(17%) and country-specific effects (19%). UV light is most strongly
associated with lower COVID-19 growth. Projections suggest that,
without intervention, COVID-19 will decrease temporarily during
summer, rebound by autumn, and peak next winter. Validation
based on data from May and June 2020 confirms the generality
of the climate signal detected. However, uncertainty remains high,
and the probability of weekly doubling rates remains >20%
throughout summer in the absence of social interventions. Consequently, aggressive interventions will likely be needed despite
seasonal trends.
SARS-CoV-2
| climate | pandemic | UV light | humidity
C
OVID-19 is causing widespread morbidity and mortality
globally (1, 2). The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) responsible for this disease infected
more than 17 million people by August 2020 (3). Much of the
world has implemented nonpharmaceutical interventions, including preventing large gatherings, voluntary or enforced social distancing, and contact tracing and quarantining, in order to prevent
infections from overwhelming health care systems and exacerbating mortality rates (2, 4). However, these interventions risk
substantial economic damage, and thus decision makers are currently developing or implementing plans for lifting these restrictions. Consequently, improved forecasts of COVID-19 risks are
needed to inform decisions that weigh the risks to both human
health and economy (2).
One of the greatest uncertainties for projecting future COVID19 risk is how weather will affect its future transmission dynamics.
SARS-CoV-2 might be particularly sensitive to weather, because
preliminary laboratory trials suggest that it survives longer outside
the human body than other viruses (5). Rising temperatures and
humidity in the Northern Hemisphere summer could reduce
SARS-CoV-2 transmission rates (6–8), providing a temporary
reprieve. Simultaneously, the Southern Hemisphere has entered
winter, and we do not know whether winter weather will increase
COVID-19 risks, especially in countries with reduced health care
capacity. Early analyses of COVID-19 cases predicted that high
temperatures would reduce summer transmission (9–11). These
predictions have been widely reported and are informing decisions
about..
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'abstract': '<jats:title>Significance</jats:title>\n'
' <jats:p>The virus causing COVID-19 has spread rapidly worldwide. It remains unknown '
'whether summer weather will reduce its spread and justify relaxing political interventions '
'and restarting economic activities. We develop statistical models that predict the maximum '
'potential of COVID-19 worldwide and throughout the year. We find that UV light, in '
'particular, is associated with decreased disease growth rate relative to other analyzed '
'factors. Based on these associations with weather, we predict that COVID-19 will decrease '
'temporarily during summer, rebound by autumn, and peak next winter. However, uncertainty '
'remains high, and many factors besides climate, such as social interventions, will influence '
'transmission. Thus, the world must remain vigilant, and continued interventions will likely '
'be needed until a vaccine becomes available.</jats:p>',
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