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Could the summer bring an end to COVID-19?

Could summer mean a slower spread of COVID-19?
(Image: © Shutterstock)

Like some other respiratory viruses such as the flu, is there a chance that the new coronavirus will spread less as temperatures increase? 

A new study has found that the new coronavirus, named SARS-CoV-2, didn't spread as efficiently in warmer and more humid regions of the world as it did in colder areas. Though the early analysis, published in the journal Social Science Research Network, is still under review, it provides a glimpse into what we might expect in the warmer months to come. 

Qasim Bukhari and Yusuf Jameel, both from the Massachusetts Institute of Technology, analyzed global cases of the disease caused by the virus, COVID-19, and found that 90% of the infections occurred in areas that are between 37.4 and 62.6 degrees Fahrenheit (3 to 17 degrees Celsius) and with an absolute humidity of 4 to 9 grams per cubic meter (g/m3). (Absolute humidity is defined by how much moisture is in the air, regardless of temperature.)

Related: 13 coronavirus myths busted by science

In countries with an average temperature greater than 64.4 F (18 C) and an absolute humidity greater than 9 g/m3, the number of COVID-19 cases is less than 6% of the global cases. 

This suggests "that the transmission of 2019-nCoV virus might have been less efficient in warmer humid climate so far," the authors wrote. Humidity especially might play a role, given that most of the transmission of COVID-19 has happened in relatively less humid areas, they wrote.

But that doesn't mean that when summer rolls around, social distancing will be obsolete and people will once again pack into bars and concerts like sardines.

For most of North America and Europe, the effect of humidity on the spread of the coronavirus would be negligible until June, when levels start to increase beyond 9 g/m3, the authors wrote. Still, with over 10,000 cases of COVID-19 being reported in regions with average temperatures of 18 degrees C (64.4 degrees F) after March 15, the role of warmer temperatures in slowing the spread might be observed only at much higher temperatures.

"Therefore its implication will be limited at least for northern European countries and northern U.S., which do not experience such warm temperatures until July, and that too for a very short time window," the authors wrote. So the chances of reducing the spread of COVID-19 due to these environmental factors would be limited across these areas, they added.

"It's unreasonable, I think, at this point to expect that the virus will quote-on-quote disappear during our summer months," said Dr. William Schaffner, an infectious disease specialist at Vanderbilt University in Tennessee, who was not part of the study. Still, "I think it might give us a little bit of hope," Schaffner said.

The spread of some respiratory viruses, such as the flu viruses, diminishes in high humidity and high temperatures. It's not exactly clear why temperature and humidity affect the flu virus or other seasonal viruses, but it's in part because when you exhale, some virus at the back of your throat gets pushed out into the air, Schaffner told Live Science. "If we were to get a microscope and look at that virus, we would discover that it's surrounded by a microscopic sphere of moisture" called a droplet, he added.

Related: How does the new coronavirus compare with the flu?

When you have low humidity in the wintertime, that sphere of moisture tends to evaporate, which "means that the virus can hover in the air for a longer period of time because gravity won't pull it to the ground," Schaffner said. But in the summer, when you exhale a viral particle, the surrounding droplet doesn't evaporate, which means it will be heavier and gravity will pull it out of the air much more readily. In other words, "it doesn't hover as long as it does in the winter," making it less likely to infect the person close by, he said.

Transmission of the flu goes down to very low levels during the summer, so we don't typically have to worry about it very much in warmer months, he added. But other viruses, such as the coronavirus strains that cause the common cold, "have a seasonal distribution that is not as dramatic as influenza," Schaffner told Live Science.

Still, "we can't count on" the warmer and humid months to slow the spread of the virus, Schaffner said. "We have to beware of wanting to walk only on the sunny side of the street — there's another side that's shadier."

Coronavirus science and news

Originally published on Live Science. 

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  • Molchanov Evgeniy
    Hello. There is information about the impact of summer on the spread of coronavirus. In these videos the author put forward the assumption about the seasonality of respiratory diseases. There is also information from Chinese virologists. q_CD5pRvBAc:1View: https://www.youtube.com/watch?v=q_CD5pRvBAc&t=1s , p-X-6ee4clgView: https://www.youtube.com/watch?v=p-X-6ee4clg
    Reply
  • Cuger Brant
    Well, i never thought i would say it but let us hope for a heatwave and all that ultraviolet light.
    Reply
  • Molchanov Evgeniy
    Hello. If you breathe air with a temperature of 36.6 degrees, it becomes uncomfortable. I understand that the lungs are a radiator for cooling the body. The SOVID 19 virus likes our radiator. It reproduces there as long as there is the necessary temperature. What I don't know. 100 percent of it depends on the temperature of the inhaled air. If we consider that the outbreak in Italy and China occurred at a street temperature of 8-10 degrees, then the inhaled air should be at least 22. This explains the fact that the virus does not get mass distribution in countries where the heat is now. In Africa and India, there is no mass infection. The reason for the appearance of infected people there may be air conditioners.
    Reply
  • jbundy48
    Here in Western Washington state and the other Pacific coast states we have one of the highest infection rates in the country. Part of what this article states doesn't apply here. That is, our humid weather is in the colder 6 months of the year, while having very low humidity in the summer, the opposite to most of the country. I wonder how this works in our situation.
    Reply
  • zinn
    admin said:
    Like some other respiratory viruses such as the flu, is there a chance that the new coronavirus will spread less as temperatures increase?

    Could the summer bring an end to COVID-19? : Read more
    Why don't scientists simply test covid 19 live virus for heat and humidity?
    Reply
  • norreber
    I hope LiveScience is not spreading around false hope. IF it is likely to slow or stop with warmer summer weather, then why is it spreading in the Southern Hemisphere? Look at the maps and you will see it is in almost every country, even across those on the South side of the Equator.
    It is Summer there.
    Reply
  • DaveC49
    admin said:
    Like some other respiratory viruses such as the flu, is there a chance that the new coronavirus will spread less as temperatures increase?

    Could the summer bring an end to COVID-19? : Read more
    It is still fairly warm (25-30C) in Australia and also fairly humid and the virus is spreading just as fast as anywhere else at the moment. While it might affect the rate a little it is unlikely to affect it all that significantly. Thailand and Singapore Malaysis and Indonesia are generally a lot hotter and more humid than most palces in US, Australia Europe, Canada and they have significant numbers of cases, particularly Indonesia and Malaysia where social isolation was started late - lower than most because of early implementation of social isolation rather than the weather conditions.
    Reply
  • DavidW
    jbundy48 said:
    Here in Western Washington state and the other Pacific coast states we have one of the highest infection rates in the country. Part of what this article states doesn't apply here. That is, our humid weather is in the colder 6 months of the year, while having very low humidity in the summer, the opposite to most of the country. I wonder how this works in our situation.

    You are confusing relative humidity and absolute humidity. A better indication of the humidity is the dew point. In the winter you have a low dew point and the temperatures can reach much lower, indicating a much lower absolute humidity. In the summer the dew point is higher, and even if your relative humidity is low there is still significantly more moisture in the air.

    You know during the day the relative humidity changes even though the absolute humidity usually does not. This is because relative humidity is relative to the dew point so it decreases as it warms up even if the amount of water vapor is relatively constant.

    Your humid weather is in the summer, same as everyone else.
    Reply
  • jbundy48
    DavidW said:
    You are confusing relative humidity and absolute humidity. A better indication of the humidity is the dew point. In the winter you have a low dew point and the temperatures can reach much lower, indicating a much lower absolute humidity. In the summer the dew point is higher, and even if your relative humidity is low there is still significantly more moisture in the air.

    You know during the day the relative humidity changes even though the absolute humidity usually does not. This is because relative humidity is relative to the dew point so it decreases as it warms up even if the amount of water vapor is relatively constant.

    Your humid weather is in the summer, same as everyone else.
    When we lived in Texas as a kid I got experience humidity like never before and never again. Constant sweating was the norm until we got air conditioning, and when we did the unit had a constant stream of moisture from the air. Once we moved back to the NW i never experienced humidity like that ever again, even when the temperature was about the same in both places. Also, dry skin became a problem that I'd never had in Texas. In the winter here we get 80+ humidity, while in the summer we can get down to the teens. Come to the Seattle area some summer and I think you'll understand. Then in winter you'll see windows steamed up a lot unless you have forced air heating. Otherwise, you'll see mold around those same windows.
    Reply
  • Molchanov Evgeniy
    The reason for the mass spread of the virus in the United States is air conditioning. Guys turn off the air conditioning, if you don't want to get sick, you have a fever now, it's healing. Do not overcool and do not sweat, I understand that this is hard, but it is a guarantee of health at this time of year. If someone knows doctors, bring this information, show them my videos. This is very important. Let the experts Express their opinion. I'm from Ukraine. I try my best to spread this information to save people. But my possibilities are limited here at home I managed to draw the attention of the regional infectionist and well-known virologist. I also managed to get through to the Institute of Virology. But it's hard for me. Just show these videos to your medical friends.
    Reply