I'll take this as a good-faith question and try to show which parts are fairly solid science, and where things have gone completely off the rails. "So what changed?"- something did. We're in a kind of "my favorite planet is Pluto" kind of situation, but this time we can't just change what words mean in order to appease people who want what they learned in grade school to stay "true". A long-held model of how most respiratory pathogens were transmitted was upended. For over 60 years, the theory was that exhaled, coughed, and sneezed droplets took a ballistic path- like a cannonball. They arced, fell, were picked up by hands, and then faces were touched, and infection resulted. If you had a little distance and washed your hands, it was felt the risk was minimal. Around 2020 we realized that this whole model was really, really wrong. This covers it quite well: wired.com/story/the-teeny-ti… Also, this paper if you want a bit of a deep dive: papers.ssrn.com/sol3/papers.… This, on its own, doesn't seem like all that big a deal- ok, they don't just drop; it's an aerosol; it hangs in the air, maybe goes further, but at first glance it seems the kind of thing a minor adjustment in infection control would address. Unfortunately, not so much- and the powers that be quickly realized this, which is why the CDC did not want to acknowledge airborne transmission, and you still don't hear a lot about aerosol transmission versus droplet. It's a bigger problem than it looks like because in the same 60-year period architectural conventions have undergone massive, unprecedented changes. As various energy crises hit, the soaring ceilings, huge windows, and displacement ventilation that were implemented after the 1918–1920 flu pandemic gave way to modern, energy-efficient buildings that were nearly hermetically sealed. Every liter of fresh air in or out had to be heated or cooled depending on the season, so ventilation was minimal. High ceilings meant lower total leasable square footage- so spaces where exhalations would rise on a thermal plume, and only settle after enough time that some significant inactivation took place, were replaced with low ceilings- where exhalations were forced to drift on a lateral plane between room occupants with little space to do otherwise. Yurts, long houses, amphitheaters, castles, almost all human lodging for a very long time was fairly well ventilated- so aerosols could escape, and pathogen loads kept somewhat reasonable. In the past 60 or so years, we made sure they could not escape. Now, in a given day, an urban human will be tightly packed in a series of metal tubes and boxes, inhaling the exhalations of easily a thousand other individuals, within seconds of that breath leaving their mouth. Potent infections spread worldwide very, very fast, and are very difficult to stop- because the entire infrastructure of our lives is basically ideal for sustaining infection chains.