1. As I said, they can tell others to stay away.
2. They provide some limited protection in that they slow the larger droplets.
3. No, they don't stop the release of virus particles. Thus, if you walk behind someone symptomatic who coughs or sneezes, you will breathe in the virus. It may be a lower concentration secondary to the mask, maybe even low enough that you won't be infected, but, again, the mask (unless it is of the correct type) has not prevented virus release.
Stay. Home. As. Much. As. Possible.
Although it is true that the virus is small enough to go through most medical masks on its own (the blue/green/white kind we wear in HK and Asia) when its sneezed or coughed out it is not floating around in the air, but in droplet form, and those DO get stopped by the waterproofed and outer layers of the masks. Not completely, but way, way, way better than nothing.
Most importantly asymptomatic people who are wearing masks reduce their transmission to others, and of course uninfected wearing masks vastly decrease their chances of getting it.
So if masks are available in a country they should be worn; the problem is that it is only really prevalent in some Asian countries. Even before SARS in Hong Kong it was common to wear a mask if YOU yourself had a cold or were sick, as a courtesy to others. Never seen that in the UK or Europe, and hence masks are not commonly available in pharmacies to the general public outside of the nations that have a supply chain.
Even here in Hong Kong we have supply issues, as in a population of 7 million, we need 7 million masks a day, which is not really sustainable, so social distancing and working from home, closing schools, staying inside, cancelling Rugby 7s etc is the other important part, which we have been doing since early February.
On another note, China claims to have first day of 0 domestic cases since the outbreak, but I frankly don't believe a word of it. Heard from friends over there than government officials have been told not to report any increase in cases at all, only drops in numbers. Having started this mess, and lied from the beginning, China is now desperate to appear back to normal and get the economy going again as soon as possible, even if it means covering up ongoing cases. Its entirely possible they will have a 2nd wave of outbreaks as people leave lockdown areas and start to go back to work.
China has started legislation to ban wildlife markets, and the wildlife market lobby is understandably unhappy, but looks like it will happen. They should have done it after SARS but were complacent, and its come back to bite them.
