Notably the US had high summer covid cases in the AC belt, in contrast to the northeast and also in contrast to canada and europe, where hermetically sealed env

Notably the US had high summer covid cases in the AC belt, in contrast to the northeast and also in contrast to canada and europe, where hermetically sealed environments are less common. I’d be curious to know what flu and cold season is like in the south. There may also be seasonal changes to hvac systems in milder climates. They all have varying degrees of recirculation vs bringing in outside air. If you are running heavy ac or heavy heating, it costs more to bring in outside air. So there may be seasonal variations in recirculation settings even within the same sealed environment. I’m less confident on this point though as I don’t know hvac’s very well and they are supposed to filter viruses.