Weather conditions drive COVID-19 outbreaks

Last modified February 8, 2021. Published February 5, 2021.
Can cold weather spread COVID-19?(AP Photo/Seth Wenig)

Can cold weather spread COVID-19?(AP Photo/Seth Wenig)

Temperature, wind speed and humidity influence how quickly COVID-19 can spread and will cause two inevitable waves of the pandemic each year in many parts of the world until the virus is contained, according to a new model based on fluid dynamics.

In a paper published Wednesday in Physics of Fluids, the professors who developed the model, from the University of Nicosia in Cyprus, insisted that climate-related effects must be included in pandemic modeling to better inform public-safety guidelines for COVID-19. 

Their epidemiological model was the first to take into account how different weather conditions affect the travel of coronavirus-carrying saliva droplets through the air. 

Dmitris Drikakis, a professor of science and engineering at Nicosia and one of the new paper's co-authors, had previously studied how weather-related factors affect COVID-19 transmission, and he was surprised that they had never been used to model the virus’ spread.

“How the temperature, the humidity, the wind can affect the transmission was not taken into account, so we thought it's a good idea to try to link the weather effects to the epidemiological models,” Drikakis said.

The novel coronavirus is a respiratory disease primarily spread through saliva droplets from actions such as breathing, talking and coughing.

Drikakis and Nicosia computational physics professor Talib Dbouk tracked how the three weather conditions affected the travel distance and longevity of saliva droplets using a computer model based in fluid physics. The droplets evaporate more slowly in low temperatures and high relative humidity, and they spread farther in high winds, according to their earlier research.

An airborne infection rate index was derived from this information and fed into a simple, widely used pandemic model. Using 2020 weather data from New York City, Paris and Rio de Janeiro, the model predicted accurately that two outbreaks would occur during the year based on the changing weather throughout the season. 

The outbreaks had different timings and “shapes” depending on each city’s climate. The model produced two distinct spikes in the spring and winter for New York City and Paris, while Rio de Janeiro in its tropical climate had one prolonged episode with two high points.

The weather-sensitive model did not precisely predict the timing of the outbreaks in these cities, and sometimes missed it by a month or more. This is because it does not account for many factors, such as public-health guidelines and the behaviors of people. It is instead meant to show only that weather seasonality causes two outbreaks regardless of other moving parts, according to Drikakis.

The airborne infection rate index accounted for properties unique to the coronavirus but can be repurposed to model any other airborne disease, which would interact with the weather similarly, Drikakis said.

Drikakis said he believes the pandemic may remain intense from the winter through the summer but that a better situation will arise by September if vaccines and other public-health measures are successful. He emphasized the difficulty of making predictions, especially as the virus mutates and many vaccines have yet to be rolled out.

The researchers argue in their paper that their index “must be included in epidemiological predictions” to improve accuracy and better inform government officials, who Drikakis said have a responsibility to understand these seasonal effects.

“Better modeling will advise the authorities to take more accurate measures,” he said. “We should not focus only on what we know so far about this but all the recent evidence, including our research, should be taken into account.”

Drikakis also called for different scientific communities to collaborate in addressing the COVID-19 pandemic.

“Historically, if something comes [from] outside the medical community, it’s not very well-perceived,” the Nicosia professor said. “I think applied scientists, the physicists, engineers and the medical community have to work together in order to look at these challenges, which are technical, socioeconomic and require a multidisciplinary approach.”

Drikakis and Dbouk have applied fluid dynamics to other dimensions of COVID-19 spread. The colleagues found in May of last year that saliva droplets can travel up to nearly 20 feet in 5 seconds in a 2.5 mph breeze. In another study, they determined face masks effectively limit the spread of coronavirus-carrying saliva droplets but do not completely prevent it.

The article, “Fluid dynamics and epidemiology: Seasonality and transmission dynamics,” was published Feb. 2 in Physics of Fluids. The authors of the study were Talib Dbouk and Dimitris Drikakis, University of Nicosia. Dbouk and Drikakis were co-lead authors.

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