Cloth masks are effective against a virus with a droplet based spread, like the flu. When an infected person sneezes or coughs, cloth face masks can contain those droplets as they spray out.

With an airborne virus you have to be able to filter the air people are breathing and a cloth face mask that isn't even fitted tightly to the face just cannot do that. This is why you need an n95 mask or better fitted tightly enough to your face to create an air seal.

For example, the Measles also has an airborne spread and the OSHA requirements for medical professionals mandate gloves, eye and face protection, and respiratory protection.

https://www.osha.gov/measles/control-prevention

Note that Flu levels hit record lows globally while Covid continued to spread like wildfire.

>CDC says seasonal flu cases hit record lows around the world

https://www.nbcnews.com/health/cold-and-flu/cdc-says-seasona...

But the truly comical part, of course, was that Covid was not acknowledged to be widely airborne until a year and a half later. At the same time that cloth masks were widely dismissed as ineffective.

Are there any randomized controlled trials which show that cloth masks have a clinically significant effect in preventing transmission of SARS-CoV-2? I haven't seen any such studies which would meet evidence-based medicine criteria, but if you know of any I would be interested to read them.

How would you design a controlled trial involving live virus transmission with a virus that is known to have long term health effects and can even be lethal?

There was one trial, which apparently later censored, that measured how mist with similar particle size behaves when it hits a cloth or other non-FFP2 or higher mask. Non surprisingly, they do not stop airborne particles that are much smaller than the "holes" in the fabric. The masks captured droplets, but later the droplets dried, split up and became airborne with very small particles.

Crickets.

It's a good placebo though.

> Which is demonstrably false.

If that's the case, be demonstrable then. Given the physical size of the virus vs the size of holes in say, a cotton mask, combined with the infection rates for the strictest masking areas, I would say your statement is demonstrably false.