Louis Pasteur was a groundbreaking scientist who made important discoveries in microbiology. His work is still very important for how we create vaccines today. Here are some key points about what he did:

1. Germ Theory of Disease: Pasteur showed that tiny germs, which we can't see, are the cause of many diseases. This idea changed how people understood how diseases spread.

2. Vaccine Development: He developed one of the first vaccines for rabies. To do this, he weakened the virus so it wouldn't make people sick but would still help their bodies build protection against it.

3. Pasteurization: Although this isn't directly about vaccines, Pasteur created a method called pasteurization. This process helps kill harmful germs in food and drinks, showing us how we can avoid getting sick by handling food safely.

4. Scientific Method: Pasteur was very careful in his experiments. He set a standard for future vaccine research, making sure that discoveries were based on solid evidence that could be trusted.

In short, by coming up with the germ theory, creating new vaccines, and using careful scientific methods, Pasteur changed medicine for the better. His work has helped shape how we think about vaccines and public health even today.