70% is "a 2m safety distance becomes some X, that isn't very easy to calculate". There's very likely an exponential fall of virus with distance, so it's probably something visibly smaller than 2m, but not by a lot.
Besides, that's hardly the only variable at play. The virus doesn't spread on the atmosphere only by dispersion, so the particles energy is relevant. It doesn't spread in only in dry particles, so that ratio is relevant, as is the efficiency in blocking the larger wet particles. And it doesn't spread only by coughing, so the efficiency on normal breathing and speaking is important too.
Also, we don't need completely effective barriers for people at the street, this is not ebola. We just need to reduce the virus spread by ~60%.
The one thing we know is that the countries where people use masks are having an easier time fighting the virus. We don't really know if it's because of the masks, but it's a good bet.
Besides, that's hardly the only variable at play. The virus doesn't spread on the atmosphere only by dispersion, so the particles energy is relevant. It doesn't spread in only in dry particles, so that ratio is relevant, as is the efficiency in blocking the larger wet particles. And it doesn't spread only by coughing, so the efficiency on normal breathing and speaking is important too.
Also, we don't need completely effective barriers for people at the street, this is not ebola. We just need to reduce the virus spread by ~60%.
The one thing we know is that the countries where people use masks are having an easier time fighting the virus. We don't really know if it's because of the masks, but it's a good bet.