The Polio vaccine is easily the most influential discovery of the last 200 years. Before then, disease was seen as inevitable, and anyone who got it was seen as doomed to whatever fate they were headed towards. However, once Jonas Salk created a vaccine for Polio, it became clear that the use of dead disease cells to create immunoresponse memory was possible, and it paved the way for countless vaccines to come about. It also reinforced the notion that science could artificially create methods of keeping people alive and well, regardless of pre-existing conditions. Due to this, synthetic insulin was created, to give those with diabetes a long and healthy life. Advancements in prosthetic technology allowed people, like my late veteran grandfather, to have something approaching normal mobility. The use of mRNA in the recent COVID vaccines will pave the way for a whole new batch of vaccines that people had not previously considered, as shown by reports that show promise for an HIV vaccine. With all this being said, my favorite scientific discovery is easily the Polio vaccine.