Hi Dr Ron,
Plainly there are various factors involved - and a main one obviously is people being close enough to each other to pass the virus on.
But as this virologist and epidimeologist asserts
"Fair called sunlight “nature’s greatest disinfectant” because the ultraviolet light inactivates bacteria and viruses. "
Which surfaces are the most infectious and how do you disinfect them? Experts weigh in.
www.today.com
so that another factor is the virus not being able to survive as well in certain environments and making it less likely to be passed on.
Of course, there are are other possibilities regarding the health benefits of sunlight in relation to viruses put forward in the original article. Vitamin D wasn't discovered till 10 years after the Spanish Flu, for starters.
And another curious factor, I was talking to relatives in the Veneto region of Italy (one of the original two epicentres) who were telling me that the big discussion point there is the observation that none of the Africans living there have caught the virus. Genetics or anti-malaria shots?
Regards,
Renato