Vaccinating now will solve problems down the road
One of the most obvious reasons to vaccinate a disease is immunity. There may be several short term side effects to the vaccine but the mild discomfort far outweighs the risk of getting a viral infection such as polio, or the chicken pox. Before the vaccine, over 500,000 cases were recorded annually. Now as few as 55 annual cases occur.
Large Scale Vaccinations
The use of vaccines can also limit the spread of a virus, or stop in an area altogether. It everyone has an immunity to the disease thanks to vaccinations, then it can't spread, and outbreaks cannot occur. Even in diseases that are nearly eradicated, without the vaccination it is possible that the virus could fight back and an outbreak could occur.