A vaccine is a preparation that causes your body to produce antibodies which will make you immune to a disease. Antibodies? Immune?
Chickenpox is an eruptive illness (you get red blotches on your skin) and it is contagious. Chickenpox is caused by a virus of the herpes family.
Snot is a thick, gooey, sticky substance produced in some parts of our body. Poses no risk to your health, but it may be annoying.