They mostly protect others, but they also reduce the number of infectious particles entering (pretty obviously). They're very leaky, so if you wear a non-respir

They mostly protect others, but they also reduce the number of infectious particles entering (pretty obviously). They're very leaky, so if you wear a non-respirator you will only delay infection not prevent one. However, if many people wear masks, there is filtration going on in both directions (at the source and sink), so they become more effective. COVID is remarkable among human pathogens because it is so damn transmissible. High percentage mask wearing completely stomps out weaker viruses (we eliminated a flu strain in 2020). COVID is almost as transmissible as measles (R0 for Omicron is commonly estimated above 8 and as high as 24), so it takes an array of countermeasures or high quality countermeasures to arrest it. Still, mask wearing will reduce the number of people infected per a unit time, making environments much safer. Now that we are in a regime where R0 is less applicable since people have some immunity to COVID, the transmission rate is closer to 1-3. This is something masks can manage to stomp so long as there is partial immunity.