The polio vaccine had nothing to do with the morbidity and mortality of the disease. Do your research. The AMA even convinced a generation that a president (FDR) had polio. He did not.
The downward trend began before the vaccine. Public health campaigns (sanitation) and nutrition were more effective and readily implemented to reverse the disease. The vaccine was an early failure ( simian monkey cancer). They battled with oral versus serum. It was all a hoax.
And it deserves an equally appropriate ending. Burn it.