I figured out why heat and low humidity reduce flu (and presumably Covid-19) infections almost to zero.
The virus’s capsid (shell) is destroyed by ultraviolet light, which is part of solar radiation. However, when the virus is in an aerosol droplet, it reduces the effect of ultraviolet light, and the virus remains active longer. Low humidity and temperature cause the droplet to evaporate faster, and heat carries the fine dispersed particles into the air (though someone’s nose might be in the way), while larger particles are pulled to the ground by gravity. Indeed, high humidity is also good – small particles are enveloped in moisture droplets and stop flying in front of one’s nose. In short, a certain level of humidity, uncomfortable for the virus, is important. However, the hotter it is, the more people prefer air conditioning and avoid going out into the sun.
Also, many think that soap simply washes the virus off, so if hands squeak after 5 seconds of lathering and rinsing, the virus is washed away. In fact, the main function of soap is to destroy the virus and reduce its ability to penetrate the cell. This function requires soap to be active for a longer time, which is why everyone writes about 20-30 seconds.
Thus, summer is better than winter, the sun is better than light bulbs, the south is better than the north, open spaces are better than closed ones, washing hands frequently is better than gloves, and a mask and glasses are better than no mask (but the point about the mask is most controversial. Simply, if someone sneezes in your face, you can throw away the mask, wash up with soap and perhaps be spared. It also prevents touching your mouth and nose)
Very interesting material, but Facebook and Medium consider it misleading. Indeed, the conclusions there are quite politicized, and it’s better not to read them. But the beginning and middle are quite reasonable. Look up “evidence over hysteria”