"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.



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."