Masks work by reducing the fraction of virus particles from an infected individual that get into the air, or the fraction in the air that get into the wearer. My understanding is that this isn’t a direct multiplier on R0, it’s a multiplier on how long (on average) you need to be around an infected person, or a concentration of aerosolized virus particles, before you’ve accumulated enough exposure to become infected yourself. Unmasked, with no immunity, the relevant exposure times (as measured early in the pandemic) were on the order of 15 minutes. Good masks for both parties would get you into the range of a few hours. Not sure how that changes with the newer and more infectious strains, but I assume the times are shorter. But basically, my take has been that if you’re going to be around someone for more than a few hours (like your coworkers or classmates), then unless you’re wearing N95 masks near-perfectly, it’s unlikely they’re going to accomplish much. Not literally nothing, but much less than they do for brief encounters.
It’s hard to pin down a threshold of a specific time of exposure because it depends on the minimum infectious dose, which varies widely among people, at least for lots of diseases. Also, the rate of shedding varies widely based on the progression of the disease, whether the person is talking, how far away the person is, etc. Furthermore, the HVAC system causes additional variation. So I think when you add all these uncertainties, a 16 times reduction in emission/inhalation would correspond to very roughly a 16 times reduction in infection, but I would be very interested to see if someone has run the math on this.
Masks work by reducing the fraction of virus particles from an infected individual that get into the air, or the fraction in the air that get into the wearer. My understanding is that this isn’t a direct multiplier on R0, it’s a multiplier on how long (on average) you need to be around an infected person, or a concentration of aerosolized virus particles, before you’ve accumulated enough exposure to become infected yourself. Unmasked, with no immunity, the relevant exposure times (as measured early in the pandemic) were on the order of 15 minutes. Good masks for both parties would get you into the range of a few hours. Not sure how that changes with the newer and more infectious strains, but I assume the times are shorter. But basically, my take has been that if you’re going to be around someone for more than a few hours (like your coworkers or classmates), then unless you’re wearing N95 masks near-perfectly, it’s unlikely they’re going to accomplish much. Not literally nothing, but much less than they do for brief encounters.
It’s hard to pin down a threshold of a specific time of exposure because it depends on the minimum infectious dose, which varies widely among people, at least for lots of diseases. Also, the rate of shedding varies widely based on the progression of the disease, whether the person is talking, how far away the person is, etc. Furthermore, the HVAC system causes additional variation. So I think when you add all these uncertainties, a 16 times reduction in emission/inhalation would correspond to very roughly a 16 times reduction in infection, but I would be very interested to see if someone has run the math on this.