Study: Temperature and humidity may indicate risk of COVID-19 transmission

key takeaways

  • A new study shows that COVID-19 cases tend to spike below 62 degrees and above 75 degrees.
  • Virus particles tend to stay longer in dry environments than in humid environments.
  • Ventilation and filtration are the best preventive measures to prevent the spread of COVID-19 indoors.

You may see a higher peak in COVID-19 cases depending on the current season, according to a new study.

Researchers have found that the spread of COVID-19 may be related to temperature and humidity. Specifically, warmer regions such as the southern U.S. may see peak COVID-19 cases in the summer, while cooler regions such as the Northeast may see more cases in the winter.

“On a cold day in New York, people like to be indoors with the heating on. Likewise, on a very hot day in Florida, we shelter in an air-conditioned room,” said co-author and aerosol researcher Chang-Yu of the University of Florida. Dr Wu told VigorTip, adding that poor indoor ventilation was to blame for the spread of the virus. virus particles.

Wu and his colleagues used data from different COVID-19 epicenters, including the United States, India, China and Germany. They found that cases surged under certain temperature and humidity thresholds, based on human behavior and how the virus spreads in aerosols and droplets.

The authors wrote that the virus was able to linger for longer in dry, low-humidity environments—especially with dew points below 32 degrees. Cases also spike when temperatures are above 75 degrees or below 62 degrees.

In environments where the temperature is between 62 and 75 degrees, which is believed to be easier for people to stay outside, transmission of the virus appears to be reduced.

Humidity and temperature play important roles in virus concentration

People release respiratory droplets when they talk, sing, cough or sneeze. These very small droplets and aerosol particles can carry and spread the COVID-19 virus in the air. They can vary in size from visible to microscopic. According to the Centers for Disease Control and Prevention (CDC), while larger droplets and particles fall to the ground within seconds or minutes of being released, smaller droplets and particles can linger in the air minutes to hours.

Humidity and temperature affect the size of virus particles and how long they stay in the air, Wu and his colleagues wrote. In dry environments, such as a heated room in the winter or an air-conditioned room in the summer, water evaporates quickly from respiratory droplets, reducing their size and allowing them to float in the atmosphere longer.

“If droplets quickly land on the ground, their chances of entering the lungs through inhalation are much lower than those of tiny floating particles,” Wu said.

People tend to release more aerosols than droplets when they talk, sing and cough, aerosol expert Dr. Jose-Luis Jimenez, a professor at the University of Colorado Boulder, told VigorTip.

“In most cases, you expel 1,000 more aerosols than droplets,” Jimenez said. “Droplets fall, and aerosols float. They behave like cigarette smoke. They float in the air, they follow the tide.”

Aerosol particles are smaller, and they stay suspended in the air for longer than droplets, but they are easily dispersed outdoors by wind and air movement, Jimenez added.

“When we’re indoors, it’s like we’re in a box. Walls and ceilings trap air, which means aerosol particles can stay in the air for about an hour or a few hours, depending on how big the place is. “He said.

The study’s authors also noted that extremely low or extremely high temperatures indicate an upward trend in COVID-19 cases. In warmer regions, people often move indoors to avoid extreme heat, while people who live in colder regions move indoors to avoid the cold. In both cases, people were transferred indoors, and they were exposed to recirculated air.

Moving indoors can lead to a higher risk of breathing air with virus-laden droplets and aerosols, which can lead to more COVID-19 cases, Wu said.

What happens to virus particles when you’re outside?

When you spend time outdoors, fresh air is constantly moving, dispersing droplets and aerosol particles.

Wu said that if someone is infected with the virus and spends time outdoors, the aerosol particles and droplets they excrete can quickly disperse and dilute.

“Unless you’re really close to someone who’s spreading the virus, the concentration of virus particles outdoors will be low,” Wu said. “If you’re talking face-to-face from a very short distance, the risk is still higher.”

Virus particles don’t last as long outdoors compared to indoors, Jimenez explained, because they have to withstand wind, sunlight, humidity and other forces that make them rot and disperse. People are less likely to inhale enough respiratory droplets that contain the virus that causes them to contract COVID-19.

“Outdoor transmission is 20 times less than when we’re indoors. The virus particle doesn’t build up because it goes up, and in most outdoor situations, it dissipates.”

Spending time outdoors with other people is a safer option, as the CDC recommends. Even without a mask, you are less likely to be exposed to COVID-19 while outdoors.


While the study sheds more light on the seasonality of COVID-19, climate and weather alone are not enough to predict future outbreaks, the researchers said. Prevention tools are still needed. For example, investing in proper ventilation and filtration is critical to preventing indoor transmission.

“If you have a good ventilation rate, the air is constantly changing, helping to reduce the concentration of any virus particles,” Wu said.

According to Wu and Jimenez, other precautions include wearing masks, opening windows, and keeping a safe distance from people. A window air conditioner or fan doesn’t ventilate the space, but it just cools and mixes the air, not circulating fresh air, Jimenez added.

“A mask or respirator is a personal filter that reduces the amount of airborne viruses that enter the respiratory system,” Wu said. “All of these are great tools to help reduce the risk of transmission in the indoor environment.”

what does this mean to you

Try to spend time outdoors as virus particles tend to rot and disperse more quickly outdoors. If possible, open windows in your home to increase ventilation and allow fresh air to circulate.

The information in this article is current as of the date listed, which means that you may have updated information as you read this article. For the latest updates on COVID-19, visit our Coronavirus news page.