Name the best known contribution of Edward Jenner.

Explanation

**Step-by-Step Solution:**

1. **Identify Edward Jenner**: Edward Jenner was an English physician and scientist known for his significant contributions to immunology.

2. **Understand His Contribution**: Jenner is best known for developing the first vaccine, which was specifically aimed at preventing smallpox.

3. **Context of Smallpox**: Smallpox was a deadly disease that caused widespread mortality before the development of the vaccine. It was a significant public health threat.

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