How many people did the influenza epidemic of 1918-1919 kill?
it killed about 20 million people worldwide
For the most part, you don't - influenza travels well on fomites and on people, so unless you keep your pig in strict quarantine for its entire life, it will get influenza at some point. The good news is, for the most part swine influenza doesn't kill the pig - it'll be sick for up to a week but otherwise should be fine.
Scientists have not found a cure for influenza. The influenza virus is seasonal, and every year the "flu" is a different strain due to natural mutations. The best we can currently do is give people vaccines which helps your body identify the virus so your body can kill them faster, and these vaccines take time to develop as it is unique to each strain. This is why you need to get vaccinated every year.