It was first synthesized in 1874. It was not turned into an insecticide until 1939. Polio has existed for thousands of years. You're right about the outbreaks, but that could be from a mutation that made it more transmissible. By the 70s we also had both the smallpox and polio vaccines and they were widespread. My mother was born in 1939. No one around her was dying of smallpox because inoculation was common and had been since the 1800s, though it was a riskier inoculation than most today. Smallpox was pretty much eradicated in the developed world. The last known case was in the late 1970s. Polio is not eradicated and still shows up, coincidentally, where vaccines are less utilized.