I think that polio was virulent before 1955 when the vaccine was developed. Now, I think, since we have developed a vaccine, it isn't as virulent.
virulent-when a virus caused a disease while temperate-when a virus does not caused a disease immidiately
Virulent are disease causing. Temperate are not immediately disease causing.
in your mouth
Well, if you didn't get the vaccine and you are around people that are infected and you come in contact with their mucus of phlegm or their infected eyes, avoid contact with you mouth or nose or you...
Polio can be contracted by contact with a person infected with polio.