No. After you get a disease like smallpox, your body is able to develop permanent defenses against it. This makes you "Immune" to the disease. This is the principle on which vaccines work.
Smallpox.
There are quite a few ways to become immune to smallpox. One way is that you can be infected with the disease Cowpox. Which is not deadly in anyway but is a disease nobody wants to have. Another way is, you can infect your self with smallpox and give yourself a mild case of it. It is proven that once you had smallpox and you survived you never get it again, by infecting yourself mildly you can become immune to it. Correction mild case of smallpox is cowpox if u become infected with cowpox u become immune to smallpox and cowpox for the rest of your life it is like a vaccination but instead of being shot with it u actually become sick but once you get over it your completely immune to it or any other more serious case of the illness.
Edward Jenner did not discover germs, he developed vaccination for smallpox (using cowpox pustules) which was much safer than the inoculation for smallpox (using smallpox pustules) then in use. However he had no idea what actually caused smallpox, only that it was something invisible in the pus from the pustules.
There are far more than two causes to that debacle. Two causes, as you asked for, are King Philips War and a smallpox epidemic.
Is sometimes referred to as the 'Father of Immunology'. Jenner's discovery 'has saved more lives than the work of any other man'
Smallpox is a disease, and is not "popular" anywhere.
Smallpox no longer exists in most MEDC's in the UN
No smallpox more deadly
Measles and smallpox
Smallpox and hunger killed more people than actual battles
It can occur more than once.
Smallpox and hunger killed more people than actual battles the Aztecs had.
Smallpox.
Because you only live once
Well, I think it is the case that cowpox is just a lesser, bovine version of smallpox. Milk maids would get cowpox simply because they were exposed to cattle constantly, much more than the average person, who was more likely to get smallpox than cowcox. A scientist called Edward Jenner observed that milk maids, who often got cowpox, never seemed to get smallpox. This was because milk maids would develop immunity to cowpox (and therefore smallpox) once they had fallen ill and recovered from cowpox. He then tested this theory on a young boy. He did this by injecting cowpox into the boy's blood stream; the boy then fell ill with cowpox. After the boy recovered from cowpox, the scientist then injected him with the life-threatening disease smallpox. The result proved his theory right; the injection of smallpox into the boy's bloodstream had had no effect on him, because his body had developed immunity to the disease. If you wish to learn more about vaccination and immunities, then research antibodies, antigens and vaccination and the way in which they all work.
You can be be exposed to it more than once
yes. enzyme can be used more than once