Polio is one of the deadliest virus to date, why, because the virus will slowly kill it's host away by suffocating it. What the virus will do is it will enter through your mouth and then start to replicate itself like all viruses. It will then clog up your wind pipe, slowly suffocating you to death. One thing that made it so deadly, was that it was so easy to catch. The virus was airborne and would spread very quickly. There was soon a vaccine that would help your immune system fight back against the virus. 1 out of 100 times the the vaccine wouldn't work. But before the vaccine was invented, there was an invention that would help the host of polio survive. These were called the iron lungs. You would put your body (except you head) in the machine and it would help your lungs to breath.