"Catching a virus" and becoming "sick" is a statistical event. Yes, you can get sick from a single virus. Highly unlikely but you can. When you are exposed, your immune system, even though this is "novel" does not do nothing. It has generalized responses. Every viral particle you are exposed to increases the odds the infection with "catch". Bunches of particles have protection from mucus and water layer of the person transmitting that can increases the likelihood of infection, hence why large droplets are more a concern.
Air does leak around the edges even of an N95, but see my first line above. This is all statistic. The infected person wearing a mask, you wearing a mask, distancing especially in indoor spaces, etc. all reduce your statistical chances of catching the virus. It will never be 0 chance if there is an infected person close, but you work to get it as low as possible. Within a society, the goal is to get the R0 < 1, which means cases are dropping, not increasing. All these measures reduce R0.
p.s. I wear a P100 respirator for grocery shopping. It's worth it just for the looks I get.
Air does leak around the edges even of an N95, but see my first line above. This is all statistic. The infected person wearing a mask, you wearing a mask, distancing especially in indoor spaces, etc. all reduce your statistical chances of catching the virus. It will never be 0 chance if there is an infected person close, but you work to get it as low as possible. Within a society, the goal is to get the R0 < 1, which means cases are dropping, not increasing. All these measures reduce R0.
p.s. I wear a P100 respirator for grocery shopping. It's worth it just for the looks I get.
Second, there is some concern that the virus is spread as an aerosol. There is no confirmation of this and even Fauci has said he cannot prove it. An aerosolized virus can linger in the air like a mist. To be protected from an aerosol you would need to have a custom fitted N95 medical mask that allows no air in around the nose and chin area and filters better than typical masks. Virtually no one has these. With all other masks, even surgical masks, air can be drawn in around the edges and thus would not protect you from an aerosolized virus.