For Influenza, it may be the seasonal rise in relative humidity, rather than increased air temperature, which impedes spread of the virus. Not because the RH directly affects the virus, but because of the effects of dry air upon the nose, throat, and upper lung tissues making them more susceptible to the flu virus.
The again, the Coronavirus is a different beast—temp and humidity may not have any bearing upon rate of infection.
I live in the high desert. During most of the year the RH is 15-20% during the day, often as low as 7%. Influenza disappears about May 15. Coincides with school getting out. But the dryness factor of membranes goes up. More people have a dry cough during the Summer. Seems to run counter to the conventional wisdom.