Ski resorts
The first big surprise for me was in March: people returning from ski holidays spread the virus!
This is not typical at all with the well known flu epidemic which also takes place in the winter period. But skiers do not usually get infected as they are out in the fresh air all day, then having lunch and dinner in the hotel or ski resort restaurants with their family / friends - with people they went with. Not with local people - skiing is not typically joined with cultural and social events with local people.
So learning that the new coronavirus is highly spreading among skiers was a huge surprise.
One of the major epicenters was Ischlg, Austria, the typical interpretation causes the bars and other entertainment facilities for the extreme virus spread. Families with children got infected, not only those participating in parties. Also, smaller ski resorts do not have this kind of night life. Restaurants where people sitting at their places do not spread the virus in this extent. Also keep in mind, that restaurants and bars elsewhere during the winter were not typical places of outbreaks.
The well known flu had not been spreading in such an extent in these ski / party areas. Why? What is the difference?
I find it a plausible explanation that this new coronavirus is much more sensitive to weather conditions than the flu. Flu is also observed to spread more during the winter - the reason is not properly understood but there are some hypotheses. Is it probable that the coronavirus also has some similar sensitivity to air conditions but in a much greater extent? A virus which spreads through the air is likely to be dependent on the quality of that carrier.
In the mountains the air is cool and humid with clouds passing by - condensation is taking place.
In my opinion, this is the key point here. The condensation.
Here are weather graphs for Ischgl in Austria between Feb 1 - March 31, 2020 when coronavirus spread was on the maximum there.
Here are weather graphs for Aprica, Italy between Feb 1 - March 31, 2020, you may try other ski areas in Austria, Italy, Switzerland.
However, this is not the case in general, here are Milan and Wien during the same time period for comparison.
Here are some news about virus spread from the Mount Everest in May 2021: