COVID transmission relies on two things. Hint: it's not weather

Human behaviour — not temperature — is driving the spread of the deadly virus.

Dave Yasvinski 3 minute read November 4, 2020
COVID-19 and weather

Early on in the pandemic, some hoped warm weather would slow the spread of the virus. Getty

Summer may have provided a welcome reprieve from the monotony of isolation, but it didn’t do much to slow the spread of COVID-19. Researchers at the University of Texas in Austin have found that temperature and humidity are minor players in the war against the virus and said the main factor fuelling transmission is human behaviour.

Their work, which was published last week in the International Journal of Environmental Research and Public Health, found that travel and time away from home were to blame for up to 60 per cent of the spread of the virus.

“The effect of weather is low and other features such as mobility have more impact,” said Dev Niyogi, lead researcher and professor at UT Austin’s Jackson School of Geosciences and Cockrell School of Engineering. “In terms of relative importance, weather is one of the last parameters.”

Many public officials — including the President of the United States — had been optimistic that the virus would dissipate, or at least slow down, once temperatures began to rise. Most of these assumptions were informed by how similar viruses behave in laboratory settings, said study co-author Maryam Baniasad, something that only gives a partial picture of how COVID-19 proliferates outside a petri dish.

“When you study something in lab, it’s a supervised environment,” she said. “It’s hard to scale up to society. This was our first motivation to do a more broad study.”

For the purposes of their analysis, researchers defined weather as “equivalent air temperature” — a combination of temperature and humidity that gave them a single value to work with. They then tracked this value alongside the spread of the virus across counties, states and countries, using cellphone data in the U.S. to allow them to incorporate travel data. Researchers analyzed human behaviour in a general sense — not as something influenced by the weather — and adjusted for population differences across regions.

Weather was found to have almost no influence across every scale examined and its relative importance was deemed to be less than three per cent in the counties they studied. While there was no indication weather impacted the spread of COVID-19, the data clearly showed the role human behaviour has played. Taking trips (34 per cent relative importance) and spending time away from home (26 per cent) were the two biggest contributing factors in the advance of the virus. These were followed by population and urban density, with a relative importance of 23 and 13 per cent respectively.

“We shouldn’t think of the problem as something driven by weather and climate,” said Sajad Jamshidi, another co-author of the study. “We should take personal precautions, be aware of the factors in urban exposure.”

The research shows the importance of examining viruses at the human scale, or at ground level where humans live their lives, Niyogi said. “COVID, it is claimed, could change everything,” he said. “We have been looking at weather and climate outlooks as a system that we scale down, down, down and then seeing how it might affect humans. Now, we are flipping the case and upscaling, starting at human exposure scale and then going outwards.

“This is a new paradigm we will need for studying virus exposure and human environmental modeling systems involving new sensing and AI-like techniques.”

Dave Yasvinski is a freelance writer with

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