With colder weather approaching and experts warning of a difficult winter during the coronavirus disease 2019 (COVID-19) pandemic, new research suggests that weather alone has no significant effect on the spread of COVID-19.

At the onset of the pandemic, some experts suggested that hot summer temperatures could reduce the spread of COVID-19, much as annual flu rates decline during the summer months. Although investigators acknowledged that weather influences the environment in which the coronavirus survives before infecting a new host, they added that weather also influences human behavior, enabling the spread from person to person.

Based on the new findings, the transmission of COVID-19 depends almost entirely on human behavior, meaning temperature and humidity do not play a significant role.

“The effect of weather is low and other features such as mobility have more impact than weather,” said research leader Dev Niyogi, PhD, in a press release. “In terms of relative importance, weather is one of the last parameters.”

In the study, researchers defined weather as “equivalent air temperature,” combining temperature and humidity into a single value. The scientists then analyzed how this value tracked with the spread of COVID-19 in different areas between March and July 2020, with their scale ranging from US states and counties, to countries, to regions, and the world at large. At the county and state scale, investigators also analyzed the relationship between COVID-19 infection and human behavior, using cell phone data to study travel habits.

Across the scales, investigators found that the weather had nearly no influence on the spread of COVID-19. When compared with other factors, the weather’s relative importance at the county scale was less than 3%, with no indication that a specific type of weather promoted spread more than another.

However, the study showed clear influences of human behavior and an outsized influence of individual behaviors. Taking trips and spending time away from home were the top 2 contributing factors to the growth of COVID-19, with a relative importance of approximately 34% and 26%, respectively. The next 2 important factors were population and urban density, with respective relative importance of approximately 23% and 13%, respectively.

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

REFERENCE
Hot or Cold, Weather Alone Has No Significant Effect on COVID-19 Spread [news release]. University of Texas at Austin; November 2, 2020. https://www.jsg.utexas.edu/news/2020/11/hot-or-cold-weather-alone-has-no-significant-effect-on-covid-19-spread/. Accessed November 4, 2020.