Okay kiddo, do you know what a vaccine is? It's like a superhero medicine that protects your body from getting sick. Long time ago, people didn't have vaccines and would get very sick from things like polio, measles, and smallpox.
In the 1700s, a man named Edward Jenner discovered that if he took pus from a cow that had a disease called cowpox and put it on a person’s skin, they wouldn't get sick from a similar disease called smallpox. This was the first vaccine ever made.
Then over the years, scientists started making more and more vaccines for different sicknesses. In 1798, Jenner made the first smallpox vaccine. It was an important discovery because smallpox used to be a really terrible disease that killed a lot of people. But thanks to Jenner, people were protected from it.
In the 20th century, vaccines became even better and more people were getting vaccinated. This helped prevent the spread of diseases like polio and measles. But new diseases like HIV/AIDS and Ebola came up and scientists are still working hard to make vaccines for them.
Nowadays, almost all kids get a bunch of different vaccines before they turn six years old. This makes it much harder for sicknesses to spread from person to person. And that's why we don't see as many dangerous diseases around these days.