Answer:
Vaccines take a long time to develop and make.
Explanation:
The cure (vaccines) to problems like smallpox take a while to develop as scientists and doctors need to make it correctly and test it correctly to see if it is a cure or not. It takes years before these things can be distributed and/or even verified for "it works!" Due to this, it may of took a century for development, planning, making, testing, getting approved and mass distributing.
