> 2. Most epidemiologists it the US, at least, believed that corona- and similar viruses were transmitted by larger droplets generated by coughing or sneezing. These droplets would not remain airborne long, resulting in the advice for social distancing and surface cleaning. The "flip-flop" occurred very shortly after it was demonstrated that they were transmitted by aerosol particles.
That makes even less sense, masks only stop the heavier droplets. The virus is small enough to go right through cloth masks when aerosols, or get carried out the sides of surgical marks by your breath.
But I remember the aerosol realization happening around summer/fall last year, way after the mask flip-flop anyway.
As aerosols you need an N95 mask to actually filter them out:
* The virus is small enough that they go right through regular cloth masks; the theory on these was that the cloth masks would catch the too-large-to-pass-through droplets and the virus would get stuck inside the droplet.
* Aerosols are as light as and easily carried by the air, which is why they hang in the air for a long period. Because they're so easily carried by the air, any mask that your breath can escape the sides of, such as a surgical mask, will carry the aerosolized virus out the sides without catching it. It's the same phenomena that stops butterflies from hitting car windows [0]. The larger droplets are like the denser bugs that aren't carried safely away by the air, those will get caught by these masks.
Really, ventilation is the best way to deal with aerosols. Open a window and get them out of the room entirely.
That makes even less sense, masks only stop the heavier droplets. The virus is small enough to go right through cloth masks when aerosols, or get carried out the sides of surgical marks by your breath.
But I remember the aerosol realization happening around summer/fall last year, way after the mask flip-flop anyway.