A vaccine can help keep people healthy and protect them from a certain virus. For example people in the United States get the flu shot when they get this shot the vaccine wont magically get rid of the virus but rather help them fight it off and protect them in the future if they keep up to date getting the vaccine
They use a formula and that formula is
People/Land Area=Population Density
Because it's lighter, flexible, and lastly it's easily to heal. Hope this helps! :D
